I think the reason that we don't do cross overs anymore is two fold.
1. We don't want to rely on someone else to give us things to do, or do things with. We don't want to rely on Gene Roddenbury, or any of his staff, to give us ships, weapons, planets, etc. We want to create a setting that is our own, unique and thriving because of what we, the players, bring to it.
2. We don't want to get into any legal trouble using things that aren't ours. It is a pain in the butt to try and write the people who own things, asking them if we can use them. I know this, because I had to do this to use some of the premises brought forth in a short lived show called Wolf Lake. People who create things like that are very touchy about where their things are used, and for what. Just like Wes would be very angry if he suddenly found out that his Nekovalkrja weapons were being used somewhere else, without that person first asking him for permission. We are trying to make something here that can be marketed to the public, and if we have any mention of things from other series we have to pay royalties, and that isn't fun.
Basically, it boils down to a wish to be unique and original. As for your posting of cross over things in the Flux board, it's difficult to say how much interest will be shown. Some things have been very well recieved and reach 10 pages in a day, other things die after a post or two.