I have basically the same set up, my 03' southwind V10 and a 20ft enclosed with a rhino and 3 dirt bikes.
Would I like more power, yup, absolutely. Is it really needed, no it tows fine a couple places up steep grades it is going slow, but no slower than the semi-trucks, faster than some.
To get more power you would need to go with a 06' or newer with a 5 speed trans or much newer 2016 for the 6 speed. To me its not worth it, these engines go 200,000-300,000 miles.
Update what you have and keep that paid off coach.