That is more of a personal preference.It doesnt hurt to frag your stuff if you dont mind,you can either sell them to local reefers or to your LFS.If you want to make room for others then sell the whole colony or just keep a small frag for yourself and grow it all over again:).Really sounds like a upgrade should take place though(how easy did I just make that sound):)
Really depends on what you like to see. I perfer a bunch of smaller/medium colonys with lots of vareity. Or the right mix of larger colonys. For me SPS is just as much about the shapes they take, like turakis, echinatas, vs the shapes with stags, bushy colonys, or tabling acros...etc
If I was to choose just a few I think I'd miss the whole reason I love SPS, the shapes they grow. If you mix them just right it can be stunning. I am not there yet in my tank, but hope that I can get it right one of these days.
I say frag up the corals and sell them so that you can purchase more reef goodies. :D By fragging and selling the corals you will be helping preserve the natural reefs and have a great method to aid in sustaining your costs.