I would mine with what youve got, and maybe buy another one or two cheap GPU's if you can find any.
As far as spending lots of money on GPU's now its a bit of a risk.
I have been mining my old rigs on and off as there have been a few coins that were ok.
There will be another coin to mine with GPU's at some point, but it might be a while before that happens.
you can always sell your gpu easily on ebay or forum or whatever you want, i would not invest very big, but few gpu are always safe they have a great resell value