OK, I have here a suggestion to 'Tune' the Cold Hearts quests.
Firstly, you meet them at Modoc, at the early-ish stages of the game (If we follow the usual Arroyo, Klamath, Den, Modoc path that is). At this point almost nobody will have the car yet, but will be on the way to acquiring it.
Anyway, seeing as their missions send you all over the place, the xp you get for each mission hardly seems worth it, especially on foot. I mean, 100XP for going from Modoc to New Reno and back? You are more likely to acquire more on the way there and back than for the mission itself.
It also kind of breaks the game order, with you visiting all these cities well before you actually have to. Off course, this makes for a non-linear game, which is good. You can also ignore these missions for now and procede with your normal game until you acquire the car and end up visiting these cities for normal reasons.
Off course, by that point most quests will be yielding you much more xp than the Cold Hearts quests.
So this is my suggestion. Each quest should give you much more xp, say like minimum 1500, max 6000, maybe increasing from lowest to highest as the missions unfolold. Depending on who you have to fight, where to go, how much to carry and so on. The one to kidnap Metzgers mum should be worth at least 10.000Xp.
That way, early in the game, you can explore half the wasteland and gain a lot of xp for what I feel is hard work and quite a risky business. (no car, probably poor equipment, no knowledge of the wastes) But, if the player decides to ignore these quests till later, when he is better equiped and prepared, the xp reward is still worth the effort and is in line with what he will be getting from other quests that far in the game.
What do you think?
EDIT: Also, why are weapons so damn heavy? I find myself constantly at odds to carry too much even with 2 NPC's because ammon and weapons weigh like a ton each. Even pistols!