Collect and keep what you like, sell/trade what you don't if you want to get more for your collection or fund more box breaks if you need to keep your funds in play (assuming you're not rich!). Follow the market and be educated so you can maximise selling potential. It's all a fun learning curve.
forums, ebay, COMC, 130point.com - heaps of resources out there.
If you don't want to pay $700 for a Luka silver prizm don't! If you like the $50 Select Silver just get that! Hype is a crazy swingy thing, you don't have to follow it. Huge demand drives up some of the card prices - some are collectors, some are investors/flippers - it's all good - there's plenty of reasonably priced stuff out there, new and old releases. Enjoy!