If married filing separately (for purpose of income-based student loan payments) but live in community property state and contribute to Roth IRA - should I file jointly?

[DanielV01]

It depends.  From a tax standpoint, it is generally more advantageous to file a joint return, and especially so in view of the complications involving community property states.  Here is an FAQ that deals with each of these questions:  

Better to file joint or separate?   https://ttlc.intuit.com/replies/3288477

Community property?   https://ttlc.intuit.com/replies/3301943

There is more going on in your situation, of course, than just the tax return.  You may want to verify what the consequences of filing a joint return are on the loan payments you mention, and whether if you file separately the community property rules affect the amount that would have to be paid regardless.  In the end, from a tax standpoint you may file either way, so choose the way that is most advantageous to your overall situation.