Moonracer has linked you to the most recent thread on the subject - as a collecting community I think most people seem to agree that Noras are the best out there for similarity to "original" although others make absolutely gorgeous alternatives.
A flutter pony with her original wings is much more valuable than a pony without her wings of course. As flutter wings are easily detached, adding wings doesnt in any way devalue a pony as a new owner can simply remove the wings if they dont like or want them. Personally however I dont think "new" wings will add value with perhaps the exception of Noras as they look so original - but if you were selling a pony with these replacement wings the value would of course be much lower than with original wings and you ll also have to make sure your buyer/bidders know that the wings are not original.