It seems to me that dispensationlism is more of a human construct and less a biblical one (not trying to offend, just my take on it).  What I mean by that is I do not see any scriptural  support for the dispensationalist application of interpretation. For example, I exclusively subscribe to the 
historical grammatical method (which dispensationalist do as well to a degree) of interpretation from Genesis to Revelation, which if followed correctly, naturally leads to the historicist method of interpreting Revelation.   I believe there is scriptural supports this method of interpretation.    I will list fifteen principals and there scriptural support.
I.  Every word must have its proper  bearing on the subject presented in the Bible.  Proof; Matt. 5.18.  [see also Rev. 22:18, 19. Matt. 4:4. Deut. 4:2. Prov. 30:5, 6.  Rom. 15:4. I Cor. 10:11, 12].
    II.  All Scripture is  necessary, and may be understood by a diligent  application and study.  Proof; 2 Tim. 3:15-17. [see also Heb. 11:6. Jer. 29:10-14; 33:3. Isa. 55:6, 7].
  III.  Nothing  revealed in  Scripture can  or will be  hid  from  those who ask  in faith, not  wavering. Proof; Deut. 29:29.  Matt. 10:26, 27. 1 Cor. 2:10. Phil. 3:15. Isa. 45:11.  Matt. 21:22. John 14:13, 14; 15:7. James 1:5, 6. 1 John 5:13-15.
   IV.  T
o understand doctrine, bring all the Scriptures together on the subject you wish to know; then let every word have its proper influence; and if you can form you theory  without a contradiction, you cannot be in error.  Proof; Isa. 28:7-29; 35:8. Prov. 19:27. Luke  24:27, 44, 45. Rom. 16:26. Jms. 5:19. 2 Pet. 1:19, 20. [see also John 7:16, 17].
     V.  Scripture must be its own expositor, since it is a rule of itself.  If I depend on a teacher  to expound to me, and he should guess at its meaning, or desire to have it so on account  of his sectarian creed, or to be thought wise, then  his guessing, desire, creed or wisdom, is my rule, and not the Bible. Proof;  Ps. 19:7-11; 119:97-105.  Mat. 23:8-10. 1 Cor.  2:12-16. Ezk. 34:18, 19. Luke 11:52. Matt. 2:7, 8. [see also Jer. 17:5-7. I Jn. 4:1; Jn. 7:24. I Thess. 5:19-21; II Thess. 2:1-13. Mt. 24:4,5, 23,24. Isa. 8:20].
   VI.  God has revealed things to come, by visions, in figures and parables; and in this way the  same things are oftentimes revealed again and again, by different  visions, or in different  figures and parables.  
If you wish to understand them, you must combine them all in one. Proof; Ps. 89:19. Hos. 12:10. Hab. 2:2. Acts 2:17. 1 Cor. 10:6. Heb. 9:9, 24. Ps. 68:2. Matt. 13:13, 34. Gen. 41:1-32. Dan. 2, 7 and 8. Acts 10:9-16.
  VII.  Visions are always mentioned as such. 2 Cor. 12:1.
VIII.  Figures  always have a figurative meaning, and are used much in prophecy to represent 
future things, times and  events,-- such as  mountains, meaning  governments,  Dan. 2:35, 44; beasts,  meaning  kingdoms, Dan. 7:8, 17;  waters, meaning  people, Rev. 17:1, 15; day, meaning year, etc., Ezk. 4:6. [see also Num. 14:34].
    IX.  Parables are used as comparisons to illustrate subjects, and must be explained in the same way as figures, by the subject and Bible. Mark 4:13.
      X.  Figures sometimes have two or more different significations, as day is used in a figurative 
sense to represent three different periods of time, namely, first, indefinite, Eccles. 7:14; second, definite, a day for a year, Ezk. 4:6, and third a day for a thousand years, I Pet. 3:8.
The  right  construction  will  harmonize  with the  Bible, and make  good sense; other  constructions will not.
    XI.  If a word  makes  good sense  as it stands, and does no  violence to the simple laws of  nature, it is to be understood literally; if not, figuratively. Rev. 12:1, 2; 17:3-7.
  XII.  To learn the meaning of a figure, trace the word through your Bible, and when you find 
it explained, substitute  the explanation for the word used; and, if it makes good sense, you need not look further; if not, look again.
XIII.  To know whether we have the true historical event for the fulfillment of a prophecy; If you  find  every word of the  prophecy (after the figures are  understood) is  literally fulfilled, then you may know that your history is the true event; but if one word lacks a fulfillment then you must look for another event, or wait its future development; for God takes care that history and prophecy shall agree, so that the true believing children of God may never be ashamed.  Ps. 22:5. Isa. 45:17-19.  I Pet. 2:6.  Rev. 17:17. Acts 3:18.
 XIV.The  most  important  rule of  all is, that you  must have faith.  It must be a faith that requires a sacrifice, and if tried, would give up the dearest object on earth, the world and  all its desires,--character, living, occupation, family, home, comfort, and worldly honors.  If any of them should hinder our believing any part of God's word, it would show our faith to be vain.  Nor can we ever believe so long as any of these motives lies lurking in our hearts.  We must believe that God will never forfeit His word; and we can have confidence that He who takes notice of the sparrow's fall, and numbers the hairs of our head, will guard  the translation of  His own word, and  throw a barrier around it, and prevent those who sincerely trust in God, and put implicit confidence in His word, from erring far from the truth. [Heb.11:6. Rom.14:23. Jms.2:26. Jn.7:16,17. Mt.7:21].
But as 
wiki points out, "
Dispensationalism is an 
evangelical futurist interpretive system for the Bible. " What I am wondering is, where is the scriptural justification of studying the bible after this fashion?
I am not sure about your idea concerning the land,  The promise was made to Abraham AND his seed, yet even Abraham nor did Isaac inherit the Land, since they died way before Israel took possession of the literal land.  As Paul writes, "now to 
Abraham and his 
seed were the promises made. " - Gal 3:16.  In Heb 11:9-10 he writes "By faith he 
sojourned in the 
land of promise, as in a 
strange country, dwelling in tabernacles with 
Isaac and Jacob, the heirs with him of the same promise: For he looked for a
 city which hath foundations,
 whose builder and maker is God."   This sound like what we call heaven to me.
p.s. The seed in that promise by the way represents Christ Himself.  "Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ." - Gal 3:16