I actually really like the idea of setting something as a 'character advancement represented on +sheet and working toward that goal', as in, setting aside advancement points or XP or whatever else you want to call the various milestones or measures of accomplishment, and having people more or less automatically progress toward that stated goal through IC actions. That's pretty frickin' brilliant.
If I was going to look at this -- and seriously, after that mention, I think I probably will look into a means of doing so -- I'd use that as a separate thing from the kind of character goals as described. Aspirations in GMC/CoD, for instance, are just 'things I would like to do'. Even the book gives examples like 'have a one night stand' as valid for short-term character goals, for instance, that are valid to character development in terms of characterization, but may be harder to directly tie into advancement-based goals.
Realistically, you could do something like 'this XP gets assigned to seduction, if you ever choose to raise it', but that starts setting up a number of very subjective XP tracks that may be hard to manage, depending on the complexity of the system.
What I can offer here is what I've been looking at. I will do my best to explain why I'm doing things this way, but I'll warn: it gets off into some very esoteric tangents. It's something also designed around the idea of the game I would like to see exist in reality, this occurring in a shared/MUX environment, and oceans of navel-gazing abstract thought time. I may miss some bits that are relevant.
My goal: a collaborative, cooperative storytelling environment in which participants can freely share creative ideas and stories and create a shared world within a specified theme and scope.
Bear in mind, this does not require a sheet. It doesn't even require a system, really, depending on the folks involved. But to make it open to as many participants as possible, these things are useful tools. Not everybody can always agree, and as a result, a system of resolution is fundamentally useful and productive.
Once you introduce a sheet, you do have the advancement question.
I am not fond of XP earning caps for the reasons @ThatGuyThere has articulated. Further, the way I have seen them implemented in the past has led to precisely what he's described. I've also seen staff slow to process +jobs screw this up even further -- where, if staff were doing their job in a timely fashion, things would be fine, but then instead they wait two weeks to so much as touch the thing, and then all that work gets capped and slashed to half of its real value. From personal experience, I can say this adds dramatically to the level of frustration an earn cap can create.
I think learning time delays are a much more reasonable thing. The potential problem you get from this is that people will potentially spend more broadly than they might have otherwise if 'I have a need to spend my XP simply because it's here' issue.
Between the two, though, I think learning times still result in the much lesser evil. 'You get rewarded for your efforts' should be a constant. 'You get rewarded for your efforts up to a point, or unless staff gets lazy' is powerfully discouraging and rightly feels unfair. The players who are the most generous with their time and are doing the most to keep your game alive through running things for others are typically the ones most hurt by this.
It's better, IMHO, to allow people to earn what they earn, but spend in a reasonable fashion. What 'a reasonable fashion' is can vary -- some things are more reasonable than others -- but to tell people 'your efforts only mean anything up to a point' is, in my view, pretty awful.