I have have both iLife 06 and iLife 08 installed on my Macbook, and to tell you the truth I feel that the applications in iLife 08 are alot snappier than those that I used to have in iLife 06. The main reason that I choose to buy iLife 08 was because of iPhoto, its the single best photo management software out there second only to Aperture.
Its definitely a good investment, I say go for it.
Its definitely not bloated, in fact iPhoto has so many more features than the previous version ever had, its alot snappier.
Here are my system specs:
Macbook (Non-Pro)
Intel Core 2 Duo 2.0Ghz
1 GB DDR2 RAM
120 GB HDD
Intel GMA950 Chipset