I popped in and read this over the holiday but didn't have a millisecond to respond.
As far as the actual card goes, what about changing the text to "collector of.." or putting "collector" as sort of a title under your name or Pauline Delaware, Collector. stylistically, I like the collector word where it is but my brain wants to fill in "of".
You mentioned one of your concerns is not being seen as knowledgeable or as being taken seriously. I would say if you start using some "lingo" with dealers, they will immediately classify you as knowledgeable. Sometimes in our minds we have the idea that people think we are time wasters, etc, when a simple asking of what we want using specific terms usually gets a dealer to open up. The average passerby won't be dropping words like crinoline, bateau, new look, or be talking about foundations. Also, many moons ago, I was nervous about appearing knowledgeable, thinking that if I was sorted out as someone who resold or was collecting a dealer would automatically raise their prices when they saw me, but I found that it was mostly all in my mind, especially at antique shows where everyone is more likely to be a dealer.
I think that it wouldn't be out of line to have printed on the back of the card the specific items you are looking for, just as said before. I tend to sometimes have a zillion business cards or lose them though. Another idea is to make up a 3 x5 card. Use the business cards for everyone, but for dealers that you end up buying from or chit chatting with that you believe will eventually have what you are looking for or develop a relationship with, hand them a 3 x5 card that they can put in their card file or pin to their bulletin board in their office. It would have all the specifics of what you were looking for as far as items, sizes etc. Maybe it would also mention more general things that you are always interested in. With the size you can go into much more detail and even mention designers or even have your photo. A business card is small and might not hold everything, and besides, its nice to have a blank area on the back for them or you to write down a note.