The DI box helps match the impedance of the pickups with the gear.
For what it's worth, I've taken a guitar straight in though an effects box. This was to create a *sound* signature as well as use the effects box as a DI. The console input gain was pushed a bit, but came out great.
If you have an amp that has a signature sound (i.e. - Fender Bassman circa 1965), I'd much prefer to mic it. But, if it is some cheapo thing with no personalized sound generating a lot of self noise, I'd try the DI approach and build up some room effects, afterwards.