I think the key factor is how much you like the present boat and
whether it meets your needs or not. If so, I'd probably go for the
upgrades for at least a couple of decent reasons:

1. You get to do it your way, and don't have to do it all at once.

2. Depreciation on a new boat will probably amount to more than your
upgrade costs within a short time.

On the down side you will probably lose the use of your boat at times
as the upgrades are being done, and poor luck or poor choices with
contractors can turn into a hassel.