So, is it just me or do kills with traps give you no XP?

That's kinda weird if so as it really limits how much I'd want to use them if I'm hurting myself in the long term by not being able to gain any experience through building and using them.

Whether they do or don't, you get the lions share of your XP from completing quests anyway, not from individual battles. I wouldn't worry about it. They can be useful for dealing difficult foes, and theres no shortage of XP in the game.

Still, I didn't manage to hit the level cap (35, right?) on my first playthrough and am hoping to get a chance to use more of the skills than before so every little bit helps.

Since there isn't actually that much combat in the game, I really don't mind grinding enemies but that means I likely won't be using traps if that's the case.

You wouldnt use them all the time anyway, from how badly it would slow down the game. Not to mention the material and weight cost of having so many traps. Theyre a situational tool, and as such, I really think you're worrying over nothing, even assuming that they somehow dont give you xp. I had no trouble capping out using traps here and there for tougher situations.

I've just seen a lot of people encourage spamming bombs and upgrading them as a valid tactic for group fights.

Not planning on doing so myself as it seems a little cheap but I was mainly just wondering if anyone knew whether or not the XP thing was true.

Bombs, yes. Bombs are very useful for handling large groups in the earlier part of the game. Not so much after chapter 1, when Geralt is much more of a badass on his own and considerably less fragile. Traps are heavy, though. It would be costly and cumbersome to carry enough around to use them more than situationally, unless you were cheating. Not to mention you can make bombs yourself at will, but have to rely on a crafter for traps.

it would seem odd for trap not to give you XP could it just be a case of creatures not being worth any
as you level up thing a worth less till they are just worth nothing

Don't think so - I noticed this at the start of my second playthrough - the Nekker cave in the Malena subquest. Killed them with the flame trap, got no XP.

Had read somethign similar on these forums before also.