Hi All - first post here of TTORA, so take this with a grain of salt.
I do a mix of 80 DIY, 20% Professional work.It started out of necessity because I couldn't afford a mechanic and had to get stuff done. Investing in a copy of the factory service manual, and learning from the online Toyota community has paid off big-time. I've done work on pretty much every system in my 2001 Tacoma TRD Off Road and I think the value in knowing how it all works together is irreplaceable.
That being said, I have also recently developed a great relationship with a couple professional technicians which have also proved to be far more valuable than the money they charged me. First was a guy ("Mike" as I recall) from Auto Rust Technicians in RI whose necromantic wizardry saved my rig when the frame rusted clean through over the rear axle. Great work, great guy, fellow 1st gen taco owner. I could never hold a candle to what he can do with a welder and sandblaster. He also had the trained eye to look over the entirety of the truck, and warranties his work against rust for 20 years.
Another story of a pro saving my ass is recently I dropped off my truck with a local mechanic to solve a few nagging problems that I didn't have time to solve (I'm in the last stretch of nursing school, so time is scarce). Main thing was my 5VZ-FE engine has had a super slow engine oil leak for about 80,000 miles. Slow enough to not effect oil level between changes, but for long enough to coat everything below the engine in oil (not always a bad thing in the rust belt). I've replaced the valve cover gaskets, and crankshaft seal which had no effect on the leak. He was able to diagnose that there was some wear on a rod end cap (i think?) from a prior owner having run it low or dry. He re-machined the part, showed my photos of what he found and how we fixed it. He was super transparent, complemented my recent timing belt job, and also replaced a number of coolant hoses for free.
I think my two cents is that doing your own work gives you irreplaceable insight into the real value of expert work. On one hand if I had a mechanic do everything, I'd be broke and would still have things to fix. On the other, if I did everything myself I would I would probably still be working on fixing things that either - I broke, don't need fixing, or would've been an easier job if only I knew to do it sooner.
-Gabe