How better to incentivize gym use...

Even some rewards wouldn't do it for me, it's just a trivial, unfun experience that lacks any challenge or thought.

That is a great suggestion, however, first they need to make battling fun again, & dare I say it, a little more challenging. After the first round of battles, even with mons on full motivation, the process is facile. The gym badge system is ok but once you have gold, a couple of extra items just doesn't cut it. I only do gyms for afew coins to keep me ticking over with raid passes, incubators or lucky eggs, it is not an enjoyable experience.

I think they messed up gym rewards by giving too many points for occupying and not enough points for taking down. But once you're gold in a gym, points don't matter much anyway.

Anyway, if you're going to give a chance at a golden razz or rare candy I'd give it for taking a gym down not showing up after and spinning.

Someone a while ago was reporting that they thought they might be receiving more 10k eggs from gyms with gold badges.

I liked the idea after you get a gold badge, excess badge experience is converted into stardust. Might benefit spoofers that hog gyms too much though. Would definitely need a daily cap on the amount of stardust from gyms at least.

Things I've thought of (not well developed ideas) for making gyms more interesting.

1. The gym system should make you hold the gym longer to get the max reward (probably pair this with also raising the reward cap). Making it nonlinear, so the first few coins come fast, but the rest of them require you to hold it longer, would probably be good.
2. motivation shouldn't start dropping on it's own until your pokemon has been in long enough to get it's max coins.
3. If all pokemon in a gym have been in long enough to get max coins, kick them all out and give a few bonus coins that don't count towards the limit.
4. Let us place legendaries - one per gym (maybe only if we are the first person to place) and only if the person placing has a gold badge for that gym. Hellooooo lugias, arcticunos and sicune (sp) in every gym! Would be fun.
5. Bring back the old gym system in some way. Maybe pokemon stadiums or some other name? Maybe these could be the ones where you could place one legendary, and keep them out of normal gyms. Have them have some other function - same gym badge type mechanic (I love that) but with a more competitive function. Maybe something where they had some bonus for people within a radius (like, the radius you can see stops around you?) who are on the same team. I like the idea of "First pokemon placed must be a legendary. Hybrid prestige/motivation system, where motivation only drops once the prestige has been dropped below some limit. Automatically award coins every night, but not very many (separate limit from normal gyms) The legendary pokemon placed could determine the effect(s) which could include things like bonuses in gym/raid combat for allied trainers within that radius, bonuses to catch/flee chances, bonus spawns (like a weaker incense?). Or bonuses that apply only to trainers with a pokemon in that stadium, wherever they are. Or even kick up the competition angle by giving detriments to non-allied team members!

Whatever we do, we need to bring back the spirit of competition, because only competition against other players gives a game lasting appeal.

I would propose a platinum gym badge, when you get that you get a big prize. Like an incubator, a 10k egg, or a rare candy (only one per gym, per day.) and it has to be controlled by your team. The platinum badge should be a hell of a grind, like 10 times what it takes to reach gold.

Should keep people interested in gyms for a while ;)

I would like it if there was some kind of raid reward when you are at a gold gym. How about a few extra balls if it was a gold gym? That would be an incentive to get more gold gyms.