I agree with your line of thinking. Yesterday I added the http://www.newvegasnexus.com/downloads/file.php?id=36432. They don't respawn, thank goodness but there are a lot more good and bad guys in the wasteland now. More Powder Gangers and more Legion, that's for sure! Last night I had forgotten I had added the mod and was heading on over to the prison and I must have killed 10 - 15 more gangers between Primm and the prison! If you like Meyers for sheriff, I would advise being careful with this mod though. It will put around 10 more gangers in Primm itself and they will all cluster around him, he dies within seconds. But when I attacked the prison it was endless, so many bodies, so much stuff to collect! So much more XP!
I've been using Increased Wasteland Spawns, mostly because of the high spawns option and that it adds to creatures as well, This morning I was ambushed by about 10 Feral Ghouls, just outside of Primm, for my level 3 sniper character whose only close range weapon was a silenced 22 it was hectic. Actually I used up most of my ammo in that fight, which reminds me of my other favorite way to raise difficulty, less loot and reduced wealth (check out harder core - http://www.newvegasnexus.com/downloads/file.php?id=35715). I think slowly being worn down by each fight is a lot better, when you weren't accurate enough in that last fight and wasted all the ammo for your favorite gun, or when you let that enemy get to close and he gives you a concussion, it makes you that much more attention in your next encounter and there's always plenty more of them around he corner.