I've kept mine and both of the captains chairs as I have visions of upgrading and know I cannot get much out of the van if it is stripped out versus being able to make it look all stock again. Regular family people want matching chairs and interiors, but that's the way it is, otherwise, you can craigslist or junkyard hunt up the back sofa bed and the mid captains chairs.
If you are only part time van dwelling then just keep it. If permanent, then you'd better have a source of cheap storage as you will not only want the room they take up but you won't want to pay the monthly storage bills. Course if you have other things you are holding onto, then you may as well put the seats with them.
I've been up here in the northwest and upper north parts of the country (Washington, Idaho) and man there are a lot of good priced old class C's and trailers up here, as well as about 3-4x as many older conversion vans than I see in Phoenix. It's a big recreation area here, trucks often have truck campers on them, every other house has a trailer or rv parked beside it... Now I know where I will come look comes upgrade time.
Been fun sitting at coffee shops on the wifi looking on various craigslist and rv trader ads... I've "bought" about 20 rigs so far, just don't have the money to pay for them...