It's entirely reasonable to do the suspension yourself. It just depends if you'd enjoy the work or not. For some stuff you want to get someone to do it, for other stuff you want to do it yourself. It's always good to shop around
Here are some thoughts: I'm going to guess that rear sag is set rather low. This lays the forks down cruiserlike which increases trail which makes it harder to turn because the ground has a longer lever to turn the wheel straight as you travel over it. Try reducing the preload which stands the rear up and reduces the front wheel trail's leverage. (Or you can lower the yokes a bit down on the forks which has the same effect by lowering the front instead of raising the rear.)
Also, I'm guessing that you're a bit bigger than the 75kg or so the stock springs are intended for (and the springs are even then a bit on the soft side). And then I'm guessing your compression damping clickers are turned in a bit to try to keep the bike up and less bottomed out.
(If this is true, then it actually doesn't work, unfortunately ... the clickers usually only affect the low-speed damping (small obstacles) and not high-speed compression (bigger hits where you stand the change of bottoming out).)
A couple of fixes are to get stiffer springs and/or revalve to get more high-speed compression damping. DIY revalving is feasible. Then with the high-speed compression damping/spring rate fixed, you can tune out the roots and rocks with clickers. Probably. Define size of roots and rocks, and your speed when you're going over them and find them harsh?
The DR-Z400 is valved kiiiiind of similar to the 70-degrees. The valving is much worse on the DRZ though
But here's a really good thread that gets pretty deep into revalving and is very informative: DRZ Fork Revalve - Shim Stack Discussion & Recommendations - DR-Z 400 - ThumperTalk
And then Shim Restackor is a computer program to simulate different damping shim stacks and suspension setup: Shim ReStackor, Finally software to tune a shim stack
... and there is A LOT of great information on the site.
Maybe it's not for everybody? Some of just just want to ride the damn bikes. But here's the info for you if you like
The Race Tech Suspension Bible is also a pretty interesting read.
And - If I knew any good suspension shops I'd mention them - sorry, I don't have anything