You won't be gaining much in actual engine performance, the 570 and 700 are pretty close in numbers. The real gain is in the ride comfort and plushness of the suspension. I can't speak about the base Wolverine but if you can get the R-spec, do so immediately. The KYB shocks are unmatched and the power steering is a must in my book.
I have 4500 miles on my Wolvy this past season and I've had zero issues with reliabilty. I've done nothing but basic maintenance and I have full confidence for as long as I own it.
The ranger is a utility machine and the Wolvy is a recreational trail machine with some basic utility built in. For light yard work it should meet your requirements unless you need the versitility of the dump bed. It ultimately comes down to what your actual needs are and what your willing to spend.