Yeah, an aluminium tailpiece will make the guitar sound more lively, and the effect really is quite noticeable - especially acoustically - but I don't think they actually improve sustain.
I often end up changing all the hardware on guitars, TonePros bridges, aluminium tailpieces, locking tuners.... but only because I'm stupidly obsessive about such things. They make a difference, but not really enough to justify the investment!
If I had the tools/skills, I'd like to just convert the stock bridges into locking ones by drilling threaded holes and fitting some grub screws to lock them. That would be both worthwhile and cheap!