For me once the GM is on board with a piece of content the players' interest in it is mostly irrelevant. They can choose to take it or leave it, and if they're happy leaving it then I'm happy letting them.
The time to change that policy is when they're NOT happy ignoring it. For example, you get your typical paladin fan who gets frustrated because their favorite class takes it in all holes on a regular basis. THAT is when you say "Listen, this other class [Crusader] does what you want, and we'll set up a simple system so that you can learn it." If they want to keep sucking after that, you can let them and nature should will run its course.
The mistake to avoid is wanting them to want what you want for their characters. If you think "it would be really cool if you played this homebrew racial class from this source" and their disinterest frustrates you, it's likely that YOU are the one who needs to try out that homebrew racial class on your own character some time. I think all GMs live a little vicariously through their players because they don't get to play when they're GMing, but they fuck it up when they start saying "no, don't do that, because that isn't what I want" whether they use those words or not. Sometimes doing the same job gets old and you want to trade places. In those cases you should go for it.
What matters is that the other players are happy doing what they're doing and you are happy doing what YOU are doing. If they don't want to branch out, then that's just their taste. I personally hate undead and aberrations. I don't like any of the fluff that comes with them and I don't want to lord over a bunch of corpses or eat people's brains. I don't want to have tentacles and I don't want tentacles to touch me. So if my GM says "You should try playing a Dread Necromancer or a Thrallherd" I'm not going to be interested at all. I'm quite content within my box, and I'll branch out whenever it suits me. I'd expect no more from anyone else.
In my home games we've completely incorporated the Tome of Battle, the Tome of Magic (aka Binder), and Magic of Incarnum. Those new systems usually come with an idea from the developer of how to simplify it for your players.
Simple systems allow players to learn and use the new mechanics without reading every page of the originating books. For soulmelds and maneuvers we write all relevant text on a notecard. For soulmelds you lay out the ones you have shaped and you get a series of small objects (I use tiny d6s, but you can use the little melted marble gemstone things too) that represent your essentia. You move your essentia around and put it on the soulmelds so that it's clear where your bonuses are (I think this is how the soulmeld cards work in the back of MOI). For maneuvers you just shuffle and move the notecards around in the way you're using them (crusaders actually shuffle and draw randomly, other people don't even need to move the cards). For Binders once you know the vestiges (Which IS a pain in the ass) you're generally not binding a large varying quantity of them, you'll be using at most 2 or 3. You learn those, and you're done.
I have less experience with 3rd party supplements, but I liked using the Book of Erotic fantasy because it gave you an appearance stat. We didn't use anything else from that book (other than metaphysical spellshaper) because you wouldn't want to, but having a 7th ability score meant I had another dump stat so I could get better stats where it mattered (when you're rolling dice you get to roll more because you have another ability score, and when you're using point buy you should get more points because you have another ability score
, dump it in both cases and suddenly your character gets a little better, if a lot uglier).