I agree with everyone else about changing it if you went to the trouble of removing it, unless you happen have one of those impellers that you can really easily inspect, like most VP stern drives I've worked on. If it only takes a minute or five to remove, re-use it and spend the money you saved on something fun, like boat gas or a nice steak dinner. I think your VP GS SX Cobra is in the subset of engines that have a particularly easy-to-service raw water pump. It's hanging way out on the starboard side and up high, if memory serves. I also recall that it has it's turned by the outer-most belt.
I used to be in the change it every season camp with my 7.4MPI, then I went two seasons just to see what it would look like; it looked the same as it did after one season. This time around I ran it for three season (and one day, the new parts had not arrived yet...). Still worked perfectly and looked good, but I don't want to risk 4 seasons and plan to change mine every three seasons now. I left the old impeller in the housing, bought a new housing and new impeller, and am keeping the old one as a spare. I carry the tools needed to swap it on the water.
