You asked if better left to a pro (a dealer tech perhaps) or a 'hack like myself'..
What would 'I' do? It can be a fair amount of work to get the trim off, then pull the instrument cluster out and disassemble to some degree the back of the cluster to get to the bulbs (althought they're prob right there on the surface and unscrew). I would pay the money to have the dealer do it. It's annoying to pay someone for work you can do yourself but.. Are these speedos mechaincal or electronic? If they're still mechanical, then there's also a cable that has to be disconnected from the back of the cluster/speedo head. No big deal, just more work.
My vote? If it's an electrical speedo and you're bored and fairly good with this stuff, do it yourself. If it's a mechanical speedo, you're not so good w/this stuff, pay the dealer. Maybe 90 mins of labor? Maybe $100? Just guesses. If you do it yourself, you've got to drive to the dealership with the bad bulbs in hand once you take it apart and hope they have them in stock? Good luck.