I will try to answer to all of you as well as I can.
See my other thread about "reworking bonuses". I think you will find it interesting...
Indeed that is a big part of my problem (the fact that I use MM1 and MM2 the most) but my rule will allow me to use these books instead of just throwing them to the trash bin if you know what I mean. Moreover, most people logically own the first three core rulebooks (PHB1, DMG1, MM1) and not the rest, so we have to find a way to apply some minor "fixes" to the game here and there in order to make the game enjoyable to people who use those books the most.
Morale rules are good and I have sometimes used them in the past.
I find 4th edition heroic tier combat faster than "heroic" tier combat of 3.5th or 5th editions, mostly because combat rules in 4th edition are clear while I find the books of the others editions a little bit messy, especially with the spells, but that probably is just me and my players. Of course, if you just create a party of fighters in 3.5th or 5th, its combat is faster than 4th. But if you include spellcasters, then it is the opposite imho. But your explanation is fair and square and I accept it as a fair opinion; but I will just keep mine opinion.
I think that, since both players and monsters can and will also use my trade-X-hp-for-X-attack-or-X-damage combat rule, encounters like those you described won't drag for too long ever again, not with my rule on the table. Or at least let's hope so. :P
I think that, with my rule on the table, both fights can be interesting because of the hp trading for damage. Of course, MV's will have more tricks and I cannot beat that, but hey, with just a simple rule I can make MM1's purple worm more interesting as well as more competitive. It is far from perfect but it is also far from throwing MM1 to the trash bin, if you know what I mean.
Your rule is interesting! I was thinking of something somewhat similar (if I understood your rule correctly) but it reduced the luck factor way too much so I left the idea.