I am very pro dethatch/power rake. Just don't overdo it.
If you have a thin layer, you can go with the less invasive dethatcher like Jeff used. Those are lightweight and pretty cheap -- so worth buying and maybe using once a year. And some folks argue (I think convincingly) that you really need to disturb the dirt more than just plugs to get good sprouting on your overseed.
For my rehab, I had to go big and rent a Clausen power rake from HD. I started with a 100% KBG lawn, and KBG is the biggest of thatch makers. I took over a decade of thatch out of my lawn -- probably the equivalent of 10 hay bales!! It was crazy -- it took days to rake it all out and dispose. Wife saw the hay pile and and concluded that I'd just killed the lawn. But it was necessary as a prelude to the over seed.
For the next couple of seasons, I plan to plug both spring and fall (CO has high clay soil). The argument there (per LCN) is that frequent and aggressive plugging will break down the thatch layer and disturb the dirt enough for over-seeding. So no additional dethatch should be needed. It looks like LCN is a VERY aggressive plugger - 2, 3, even 4 passes. If I don't do the plugging myself, I tip the plug guy very generously to make sure he doesn't give my the once over lightly job.
Since I still have PTSD from the power rake episode, I'm trying to just rely on plugs (no raking required). I'm also adding fescue/rye seed to move away from 100% KBG -- mostly for less water but also for less thatch. So it looks like I'm working towards what the JG Ultra is -- KBG + fescue + rye.