I just bought 60 new gretchin.

The old ones, not the new ones, so they aren't as varied and cool. Gretchen do a few things very well and are cheap. You can field a unit of 29 Gretchin and 2 Runtherders for 107 points, and that's 31 models that you can do a LOT of things with.
1. Screen them across the entire front of your army to provide a 4+ cover save to everything.

Your grots should even be tall enough to cover 50% of the front of your trukks!!!
2. Run them onto an objective that you have strategically placed into cover. They can go to ground on it and hold it against ridiculous amounts of fire (going to ground gives +1 to cover saves). You end up with a 3+ cover save. I use this tactic quite often! I have a huge mob of gretchin sitting on an objective and my opponent drops templates on them. *laughing* I act all sad too, like "Aww..what did they ever do to you?" when in reality, I'm quietly dancing that they're shooting at my gretchin instead of my orks.
3. Gretchin aren't fearless, but your Runtherders are.

They make your gretchin fearless until they die - they bzap the little gitz with electrical prods if they dare think about running away.
4. Use them to assault and tie up a fearsome enemy. Things that spell doom for Orks (even nobs): Abbadon+Possessed marines, Assault terminators, assault marines....you can use the rules to your advantage. If you assault one of those units with your gretchin or make those units only able to assault your gretchin, the next turn you can counter-assault their power unit with your own orks. According to the rules in this kind of complex assault, his unit must still attack the gretchin (except for his models that are in direct base to base contact with both units).
I've done that before too. I was playing a chaos player who brought Abbadon + 10 possessed marines in a land raider. Abbadon gets 5-11 attacks per turn (5+
D6), and they're strength 8 power weapons. Even if you have a group of nobs, or nob bikers....every time he causes a wound, a nob dies. Its ridiculous. On top of that, his possessed marines rolled for a power and got a 6 which means that they ALL have power weapons. Any of my units would straight up die trying to fight these guys.
So what I did: My gretchin mob made a circle around these guys so that they only had one assault target, which he assaulted (if he didn't, I would have assaulted him). While Abbadon and his cronies were wiping swaths through my gretchin, Ghazghkull and my nobs came in on the charge next turn (on the Waaugh!) and counter-assaulted. I arranged it so that Ghazghkull was in base contact with Abbadon (Ghazzy has a 2+ invulnerable save on the Waaugh) and only two of my Nobs were in base with his possessed marines. You can imagine what happened next when Ghazghkull's 7 powerklaw attacks and my nobs with 3 powerklaws and 3 big choppas went to work.
So yeah - gretchin have their uses.