I've been a GURPS GM for two decades now. I never thought in terms of "conditioning" people towards a more complex version of GURPS.
Yeah, me neither. GURPS has been my system of choice since the mid-'90s, though I've certainly played plenty of other systems.
I long ago stopped expecting my players to completely digest the rules of whatever game I'm running. When I began recruiting new players (non-gamers) to join my RPG groups, I discovered that for most RPGs, the game rules form a real barrier to entry. I experimented with rules-lite games like Fudge, but we found that these systems weren't satisfying for long campaign play and they irked the more dedicated gamers who enjoy the crunch. In response, I just pushed the rules completely into the background. This is still my go-to method.
I work with new players to develop a character. If they're into the rules, I let them have free reign. If they aren't, I just ask them questions and build the character that they want to play. During the game, I simply ask people what they want to do and apply the rules that make sense. I always explain the mechanics that I'm applying in a conversational way, and I'll let a player back out of something that the mechanics don't support. Most players begin to learn the rules and end up borrowing or purchasing books themselves, but I don't expect or require this. Some people enjoy learning the details; others just want to enjoy the immersion and don't care about the books. This has been true with both GURPS and D&D (among other games), though I was surprised to find that GURPS, despite its potential complexity, makes it easier for me to keep the rules in the background because it is built on a more simulationist core.
A player came up with a character concept who could be described as a specialist bare-handed wrestler. That was why I introduced more detail as to close combat and bare-handed fighting, and eventually GURPS Martial Arts. Another player loved his character's brute strength and greatsword and he never cared to learn the subtleties of close combat; actually his standard tactics was to avoid close combat.
So the first player learned the details and maneuvers and tricks, the other player did not and simply trusted me and the first player to handle all of that.
I have had this same experience at my table. Some players want all the grit from
GURPS Martial Arts. Others just want to swing their swords. I make sure that things stay balanced so that both characters can be equivalently competent.
In short, it's the players driving the amount of complexity, not me (the GM). They want it more complex, it can be more complex. They want it simple, it can be simple.
This is easily done with GURPS, by the way, because it's not just universal - it's modular.
I've found this to be true as well. Have you tried
DFRPG yet? It's a great system for new players who want the standard D&D-style swords and sorcery genre with GURPS under the hood. We picked up a few boxed sets for our middle- and high-school RPG clubs and they've been quite popular.