I think its a two fold problem really. Paid mods don't often do well because people don't want to pay for something, they want it free, then those with free mods who use a copyright removal system as payment, people think paying to remove their copyright entitles them to some type of extra support.
Then donating, which I cannot comprehend why donating would give you any more right to responses than someone not donating? Donating is different to paying for a service. I think people need to get a grasp on the reality between the two IMHO. The XF dev rating system will sort most of this out IMHO.
I would love to see the XF system incorporate an ability for the dev to just implement directly with a payment button from the page, so we don't have to go across to some other site, and instead you can buy mods directly from the developer here through their paypal, with support all in one location, then we can use the rating system XF have incorporated to rate mods and their developers so lots of customers don't get sucked into bad developers dash for cash, then do nothing for it.
I feel if you donate (or someone donates to me) that I owe them a bit more in the way of support and attention. This is not to say that I'll ignore other users, but I'm going to be thankful to someone who has donated, and I'm going to show it through being attentive. If they've got a specific request, and it involves something in scope of my vision for the modification I am more likely to do it than if it were something suggested by someone else.
While many people here suffer from overblown entitlement when they donate, they are allowed it to some degree. Donations are what allow coders to release add-ons for free; without them many will not do any work (unless like Kovifor they have a passion for it, which most do). Donor only becomes an issue when they become abusive, or they become overbearing and throw it in your face (not necessarily abusive). That makes you lose your drive, and you just don't want to deal with the crap anymore, causing you to become lax with your modifications.
On the other side of the fence though, there are developers who will always treat their users poorly, whether they've donated or not. I believe if you release your work you should weigh any suggestion with a bit of consideration, even if its obviously pointless to you (it might not be to the poster). I also can't see how donors are treated the same, if not worse than other users. Its basically shooting yourself in the foot because you're never going to get donations from that user again, and it might feedback into other potential donations.
As for paid add-ons... I really feel only things that take a bit of time should be paid. If you can do the add-on in 1-2 hours, charging for that just seems like you want to nickle and dime people (I've recreated a few add-ons here I needed for my site with more features because I won't pay into 1-2 hours of work). This is always the developers choice, but its also something that'll effect how they're viewed by the community.
To be completely on-topic, I have to say I rarely donate for free modifications (haven't yet as I haven't even launched my site yet), and the ones that do are ones of coders I respect, and who provide excellent products and support.
Do I feel guilty about not donating to the others? Definitely not, as donations are not a requirement, they're a sign of support. Just as donors are not entitled to everyhing the may wish, developers and designers are equally not entitled to donations from everyone (And I believe this for my own work as well).
People should only donate when they feel a donation is deserving, not just because developers try to wheedle extra money out of them. Donations happen when you provide excellent modificaions, and great customer service, anything less is disrespectful to the donor.