The Simplicity will hold up great as long as you take care of it, perform regular recommended maintenance as suggested in the manual, and/or don't let any kids use/abuse it like a go-cart or 4 wheeler etc.
They have heavy built frames and transmissions in them. The decks stripe as good as anything made. Opt for a Vanguard engine if at all possible.
As for the front mount blower vs the separate WB unit- the attachment won't be cheap, but then, neither will a decent quality WB. You can always use a dozer blade instead of a blower, and also use it to move light dirt, gravel, mulch etc as well. The Simplicity has a limited slip rear end as well as a diff lock pedal, so traction is excellent. It will be lighter and easier on your turf, and with a 54" deck, it will make pretty good time on your lawn.
I demo'd a Gravely pro Stance stander last year and the build quality and cut are excellent, but the stander is actually harder on my back than the ZTR's are. That is something else to consider- with a Z of any type, the tendency to go fast is always there, which leads to reduced useful life of the machine, and a lot rougher ride than a GT gives.