Dragonite...should i bother

Best defender moveset. If you have the candy I would.

An 87 IV Dragonite CP at level 30 is around 3025
A 100 IV Snorlax (next highest max cp mon) CP at level 30 is 2876

So unless the gyms around you are all Dragonite, I would say yes.

Dragonites are not good defenders. They are only good for a high position in the gym because of their high cp.

So, when you attack a gym, have you ever run away or quit because of the moveset that one of the defenders has? Or do you just use an extra potion/revive and power through? If you, like the vast majority of trainers here, simply take down whatever gym you've set your sights on, then the defenders moveset DOES NOT MATTER (ok, slightly more or less annoying but not a game changer).

For defense, CP potential is far more important than moveset, unless you just want to have the textbook perfect moveset (in that case, who cares what we say here, you already know your answer; likewise if you have a floor for IV's of mons you power up).

So it really just boils down to if you want/need a 3K+ defender - I have none at level 32 so I damn sure know what I'd do!

Lapras wipes him out so fast either way. Rather have a jolteon (gyrados slayer).

The reason why you're seeing mixed opinions is because these questions are really case-dependent and people have different needs! So there is not and never a standard answer.
What I know is that:
Is Dragonite a solid defender (hard to defeat)? No;
Does Dragonite get high gym placement? Yes. In your case, yours will have higher CP than any other species 100iv mon at the same level!
Therefore:
If you want to top gyms, power it up;
If you want to build solid gyms (usually with collaboration), then choose Snorlax/Lapras/Chansey, or even Vaporeon.
Hope that can help.

If he's your only Dragonite I wouldn't power him up. Will seem like a waste to then have him just sit in a gym, locked to you. Save for a second Dragonite and hope for a good attacking moveset you can have fun with.

I just (yesterday) hit level 32 and I have two Dragonites:

2837CP, Level 30'ish, with Steel Wing and Hyper Beam. I use him for Defense. He's been at the top of a gym for about two weeks now. I'd say it's because he's an awesome defender, but how would I know....we can't see the battles. Probably has more to do with the many Snorlax, Rhydon, Vaporeon, Gyarados, and another Dragonite sitting below him and a semi-hard to park near gym location. I guess having him sit in a gym is supposed to be a good thing; but makes you start wondering if the daily payout would have been worth a lot of candy&stardust to power up for a high gym placement?

2900CP, Level 30'ish, with Dragon Breath and Hyper Beam. He's a go to Attacker for me in most gym battles! Dragon Breath is awesome!!

And while I do think a "perfect" moveset is mostly for perfectionists and number crunchers, there does seem to be validity to some sets being much better for attack or defense than others... as I found with this SW/HB being not great when attacking....especially after I later saw Dragon Breath in action.

I'm only 4 Dratini's away from evolving a 3rd Dragonite! And at this point I'd rather use my candy to get another Dragonite than power up the ones I have. In fact, I specifically chose high level Dratini's to evolve even though they had lower IV's, because I knew candy was hard to acquire and I wanted the Drag's immediately usable, and then more Drag's sooner (My first one has 16of45 IV and the second has 21of45 IV; and they still seem to work fine.)

SW Aragonite are good defenders.
SW/DP and SW/DC are the best two defending moveset.

You can power this one with no hesitation.
But try to get a DB/DC one before powering this one above lvl30