Its all according to your money situation. You could probably sell your motor for $3,000 or so, but then a new 200 will cost you at least $13,000, so how will you pay for the new motor. I wouldn't recommend taking out a loan for a new motor, especially if you are still paying on the boat, but then again, I dont ever recommend taking a loan.
Another option would be to buy a used motor. You can get a 2003-2005 Opti for about 5k-6.5k. Four strokes are going to be more expensive and not really offer any advantages except no oil. The reason your GT has such a hard time starting is because its a carb motor. An Optimax is a EFI which will start super easy.
Last recommendation would be to buy a 200. Dont settle for anything less or you will regret it in the long run.