Alas, I have not been riding my 2000 like I should (in my defense, I've had seat time off the road on a KLR for the last couple years). As a result of my negligence, I think it sat too long and the fuel maybe went bad.  It was a really rough and smoky start at first, but eventually it cleared up and started revving up, but when I cut the enricher, it dies completely. Same if I give it basically any throttle at all. Was hoping a pro here might help with a diagnosis?

I did try and let it run for a bit with a fuel additive, but didn't help.

Thoughts on some things to check for? Any additional info that might be helpful?

Two years of sitting with untreated fuel?!?! You'll need to tear down the carbs and  manually clean them.

Siphon the old gas out, add new gas, drain the bowls... You never know - it might clear itself. Go easy on chemicals - too much can damage carburetor internals. 

An optimist, eh?  LOL.  The carbs are going to need to be cleaned out as well as everything else associated with the fuel system. 

Very doubtful that a drain and flush or a drain and add chemical will do anything.
The low speed jetts and passages are probably blocked.
And/or the float valves are frozen.

Ride safe, Ted

Start with the easy things. A couple of gallons of gas is what.. $4.50? It worked for me once.

clogged pilots. time to pull them for sure.

If yer lucky, it's just bad fuel.
If yer not, then the carbs need doing.
Personally, after leaving her sitting for that much time, I'm betting fresh fuel will improve it, but you will still end up needing a carb clean.

I've seen this many many times since 2009 when I started fixing bikes for people. It's plugged idle jets. The gas in the carbs always gets rotten and the jets get varnished. The only way to fix them is to take them apart. If the tank was over half full that gas is probably okay. If you bring me the bike I'll fix it for you for $27/hour, usually $200-$300. That would include pulling them, fixing them, reinstalling, and tuning. A petcock repair or tank cleaning or other repairs would be extra. They always run real nice when I'm done.