The issue is not exclusive to Winamp, it happens a lot lately with laptops and newer devices which no neccesarily have bigger screens but it does have bigger resolutions (that was a correspondence mantained some time ago but not anymore), specially with legacy apps, like Winamp.
In short, the best alternative offered lately is to find other skins that suits you which are made "gigantic" on purpouse, like:
Komodo X Touchscreen
Quinto Black CT
And some others I don't remember now, search on this forum, you'll find similar threads asking more or less the same.