ya, there are advantages to both,
4th gen pros:
-lighter
-potentially cheaper (older)
-easier to swap legit (since you can use any newer engine, unlike a the 5th gen where you can only use newer from 92-95)
-simpler to work on (older, less electronic, OBD-0)
5th gen pros:
-more safety features (airbags, if that interests you)
-more feature on some models
-as you mententions, no need for aftermarket mounts for B series applications
-if you get an Si or VX you don't have to worry about vtec wiring
-newer car (slightly)
-you could get a coupe if thats cool to you...
after saying all that, I still think 4th gens are cooler, if your really into performance, spending a few hundred extra for some quality mounts shouldn't really bother you, and you will get a lighter car (that is if you go with a 4th gen)....