Cool topic Brian.
While I do like the OT stuff a bit better, I army build more with the PT stuff.
My reasononing might be a bit different than others, but what drives me to buy more PT army builders is the fact that we see larger battle in the PT, with more of an emphasis on large armies going all out. We see thousands of troops in so many different scenes... The troop battles in the OT seemed more confined with smaller fights going on (of course because of the limits of technology those days) for the most part so I guess that's why I don't go as crazy with my OT armies.

Yes, I have to agree with this as well.
I tend to build how you see them on screen.
There were MANY Utapau troopers, hence I have a huge Utapau army.
Many 501st troopers.
MANY MANY AOTC styled troopers.
While I have a lot of Stormies, I don't need a huge army for each scene. Only really big land based battle with Stormies is Endor. Snowtroopers only appear on Hoth, and at that you don't really see too many of them, so while still an army, it is much smaller. Biker scouts even less as they were only on Endor and not seen too much during the big battle.
What I do like about that though is that you can convey the scene very well with a dozen or so troops and still make it look good. Exception again being Endor. Nearly any given OT scene with troops can be done with a dozen of so troops and will look like it's fleshed out well. Heck with the Death Star there are Officers, Gunners, Death Star Troopers, Stormtroopers, and TIE fighter pilots to fill scenes. With that kind of variety we really don't need to have tons of each. (Though trust me I understand the desire to want a lot.)
But to do something on the order of Utapau or better yet Geonosis, well a dozen just doesn't cut it. Well, not with what I have in mind, mind you my diorama plans call for each of those to be LARGE dioramas at 8ft wide, 5ft tall and 4 ft deep each. So it stands to reason I need more troops to fill those dioramas up.
Large OT dioramas just don't call for that kind of amount of figures. True enough a multifacted Death Star diorama would need many Stormies to fill it out, but that's more like many smaller diioramas put together than one big one. I have plans for this too, but it is modular in design to allow for change.
Anyway, that's my two cents.