Upgrading the graphics is worth it if you want to use RTG software and make Workbench nicer. However, TBH with an 030 I wouldn't bother. Much of the software which needs RTG won't run particularly well on an 030 (I'm talking games here. RTG apps may be different depending on what they actually do).
IMO if you're thinking of upgrading your A1200 to a tower, you might also want to think about selling what you've got and getting an A4000. The expansion potential is much better, and I have found my A4000 to be more stable than an A1200T + Mediator.
--
moto