cjpalermo1964, regarding paying the "graded tax", my only caution is that because of the pricing differential between graded XF+ and ungraded XF+ stamps over the last decade or more, I'd be skeptical of any ungraded item that should grade 90+ (and "very" sketpical of anything that should grade 95+). Those ungraded gems are still out there, but in general, those that "could" have been graded were graded (because they were immediately worth 2x-10x more). I have no way of knowing how good you are at detecting hidden faults and excellent repairs, but I'd suggest you send a couple of your ungraded gems off for a cert (graded or not) just to make sure you're not getting duped.
Unless there's a good story as to why an XF or better stamp has not been graded (or only has an "old" cert), my advice would be to assume that it has some sort of problem. If only I had a dollar for every collector who told me about the steals they got buying ungraded/uncertified gems at bourses, at auction, or on eBay
, but actually had an album full of faulty, altered and misidentified material that was only worth a small fraction of what they spent... Caveat emptor!