LEGO VIP is an AWESOME deal, as every dollar you spend gains you a point, and for every 100 points you get you get a $5 off coupon you can use whenever. The only negative is that you're limited to buying from LEGO's website or LEGO Stores, and they don't put much on sale like brick and mortar stores do. But the points add up quick. I bought the UCS R2-D2 in May and that was almost $200, and with some Marvel stuff I bought, I have $10 waiting to be used.
As for getting old sets, it's tough, because once a set goes out of production it's pretty much gone forever and if you missed out, prepare to pay a bundle. So you're pretty much SOL on those.