Are you noticing any negative impact in play yet? That's really the thing that should guide you, imo. In my (kinda-limited) experience, nothing particularly bad happens when some characters are way ahead of others; if you hit the long game, it's kind of expected, actually, with new characters being brought in halfway through.
Might be worth asking around the table to see how the group feels, though, for two reasons:
1. Some folks actually enjoy falling into a bit more of a "supporting cast" role, so spotlight time may not be as big of an issue as it seems.
2. It's a good opportunity to talk about what they're highlighting and why. Sometimes it's easy to forget that you don't *have to* highlight the Gunlugger's Hard or the Skinner's Hot every session just because that's their shtick, for instance.
(Aside: sometimes, one of the best things you can do for a Battle-hardened Gunlugger a few sessions in is to highlight their Cool and say, "You're a badass, but I really want to see you be a badass in a ROAD WAR!!")
If you're looking for a rules-hack fix, I cribbed this from an old thread on here. It's a simple tweak that squares up advancement and reduces roll-mongering a bit.
• Highlight stats as normal, but don’t mark XP for rolling a highlighted stat.
• At the end of the session, ask the group the following question for each of your highlighted stats:
— Did I show you how [stat] I can be? Alternatively, did I show you what happens when I try to be [stat]?
If at least one player answers yes, take 2 XP.
Playing this way, the seduce/manipulate "stick" becomes truly powerful, and players typically gain 2-5 XP per session (4 max from highlights, plus stuff like insight coming into play sometimes).