Platinum is worthwhile if you are flying enough to retain it ...
After 9 years of WP I dropped back to LTG in early 2011, and I haven't looked back, although moving helped me overcome the "need" to fly QF.
I'm also philosophical about the F lounges, yes they are nice, but ultimately I've found I am less tempted to get to airport early for the F lounge (so have more time at destination or home) and whilst the food is good, it's not as if I can't afford to go to a nice restaurant and have even better food. In MEL anyway, the EK lounge is a reasonable substitute anyway, if open. And here in SIN, we don't have FCL.
Probably the things I miss the most are ability to request awards (although my last few before I dropped to LTG were denied anyway) , free access to exit rows (axed), anytime access to lounge (axed), and most importantly the shiny card to show off to others (joking on this one
).
If flying mainly domestically, or domestically + US travel, VA Gold is good to have to supplement LTG, if flying mainly to Asia/Europe plus domestic, then VA Gold or SQ Gold. Of course with a credit card Priority Pass as well.