I would say that very much depends on:
1. location, which part of the state
2. location, which side of the house [N, S, E, W]
3. your potential usage, your desires, your lifestyle
4. possible return on investment - in enjoyment and/or resale
Living in NE section, a 4-season room or a sunroom I have been told by 5 different contractors that such would not be good use of funds. So, I added a room, an addition to the house - have pool table, stereo, and foolsball table in there, along with some plants, etc. Now, on the back of that [which is facing east, towards a field through my pines], I've a porch, that may someday screen in to minimize the damn flying blood suckers. With that said, I would still love to have a sunroom on the south facing side of the house, which would then be between house and pond. But, w/ the price of petrol going up, will probably need the funds to pay for means to get back/forth to work!
ps: make triple sure that what ever you buy/build that there is 100% guarantee of no water leaks. My FIL had a 4-season room put on [this is in Ozarks of Missouri], and they are fighting water leak problems...

Remember that water will find the path of least resistance, and time is on its side.