Are driver tubes as critical as gain stage tubes?

For me all tubes are equally important.  I have actually had more headaches with the voltage tubes (drivers) than with amperage tubes (the big gain tubes).  

For me it depends on the actual application for that particular driver tube. So do I need trace matched or not , depends on the application. Recently I’ve been tube rolling with the 12AX7 phase tube that feeds the two 12AU7’s in my mono blocks. What I’m finding there is I’m better of going to a lower mu substitute which lowers the noise floor of the amp. Although my pre has five gain settings in addition to the actual volume control , the lower mu tubes ( 12AT7, 12AY7 ) make a noticeable difference. Cheers , Mike B. 

Normally, they shouldn't matter match, but it depends on how advanced and "finished" your system is. If your system is advanced and if you have spent lots of money on it to make it sound nice, even driver tubes will matter much. Otherwise you should be OK :-)