I'm not a DVC owner, but I'd like to chip in from the point of view of someone who could be invited, rather than someone doing the inviting.
If I go on a road trip with someone (not a family member) in their car, I'm going to offer to pay for the gas — all of it. They bought or leased the car, and they're going to have to cover the wear, tear, and mileage on the vehicle that all driving, including this road trip, will slowly and gradually contribute to. The very least I can do is cover the only concrete and in-the-moment cost. Splitting gas evenly wouldn't be sufficient, since they're already absorbing so many other costs. I've made that request of others when we took my car, and no one ever batted an eyelash at it, and I'd insist on it if we took theirs.
Likewise, if someone (besides a family member) invited me to stay at their DVC property with them, I'd expect them to ask for some kind of compensation. Just because they've already paid for the points doesn't mean there's no value to them: If I weren't enjoying part of that value, my hosts would either have the room to themselves or be paying for a smaller space.
At a bare minimum, if my partner and I were invited to someone's DVC property, I'd want to cover all the groceries and any restaurant meals we ate together. I'd insist on it, and we wouldn't come if they didn't say yes.
This, in my opinion, is equivalent to paying for gas on a road trip.
If they let us and gave us the figures for it, I'd offer to cover anywhere from a proportional share of that year's MFs to an equal share of that trip's point usage. This is true whether they upgraded to a larger room for us or if we're just more people sharing a smaller space. Money has value, but so does comfort. Of course, I say all this partly because I've been researching DVC and know how much it costs. Someone who doesn't know that can't be blamed for not offering much compensation, but now that I know, I could never accept an invitation without discussing ways to return the generosity.
I respect that a lot of folks just want to share what they have, and that's beautiful and kind. But too much giving can make recipients feel indebted to you, and for some, that's a very uncomfortable feeling. Allowing people to reimburse you can also be a kindness. I definitely understand not wanting to demand compensation, but, one, it might not be as awkward as some may think. Some guests might expect or welcome the opportunity to repay you at least a little. And, two, if they offer reimbursement unprompted (and you know they can afford it), please just accept it. That warm feeling you get when you offered to let them stay with you? That's the feeling they deserve to experience when you accept their offer in return.
That said, it can also be a case-by-case thing. If your guest is a next-door neighbor who happened to mention in passing that they'd like to see WDW, it's more appropriate to open the gate to compensation than if, say, your guest is your kid's friend's parent who just lost their job and you want to lift their spirits with the gift of a memorable time with their child. Many people in this thread also make the distinction between family and friends or between people they invite and those who invited themselves.
There are so many thoughtful and giving people in this group, and it's really inspiring. I just wanted to suggest that it may be in your guests' interests sometimes to let them give back and even to open the door for them to do so.