I believe that you will get discounted. Not exactly sure how they work it as it seems to differ for each sale/person/situation. At least that's what I have been able to figure out. I have bought some of the SSL stuff as single plugins, and have upgraded to the "collection" to included all of them at a cheaper price than full price.
Check this place out. Some of the most knowledgeable people about UAD plugins and hardware visit often. They would have the best info on your question. Seek out Matt (guy that runs and sponsors the forum, it's not owned or run by UA), and UniversalAudio who is a official UA representative that visits the forum. You may not get an immediate answer. It may take a day or two.