Is Blissey worth the dust?

If you have the dust, I would at least bring her to lv30, for the sake of holding gyms in clutch situations, such as before an EX / legendary raid begins

As most nowadays probably have good counters, a strong Blissey will probably not deter people from taking down a gym.
In that sense, it doesn't matter if it's a level 20 or level 40 Blissey.

But, like EruptHonorFace said, it can be useful in situations where you need a Pokemon that can defend a gym just before a raid.
Also, if people don't have too much time to take down a gym, they might give it a miss if there's a really strong Blissey in there, especially if there's other strong Pokemon there as well.

Personally I rarely skip a gym just because I see a 3000+ Blissey there. It's only when I really do not have the time that I move on, but that doesn't happen very often. And with great counters a Blissey won't last forever.

Depends on your local community. If you can toss a pidgey into a gym and expect it to sit for two days, there's basically no reason to invest in defenders. But most players have absolutely no way to defeat a high-IV, max level Blissey, and he's an absolute wall if you are in a place where turnover is high and you need to defend with golden berries.

If you don’t have a good blissey then absolutely. Many others will say No but consider this
A Maxed out blissey with good iv (3100 Cp & up) is not a simple task to kick out if you are feeding golden berries and the attacker is alone especially now with potion drought.

I would personally take it all the way to 3215 CP, Level 40. You’d be surprised how many players will still time out on it.

I am currently still powering up Hooh, if no other project, then will go back to Blissey!

I hatched the same egg 8 weeks ago, haven't done anything with it except TM to Z/DG...I do have 4 other 2700+ Blisseys...and 170 golden berries, yeah gonna wait a bit longer

She's definitely worth the dust; it's just a question of when. If you have other more immediate uses for dust, the Chansey will be there to power up later. If you have more than enough dust, go ahead and do it now.

It's only worth the dust if you live in an area with a relative high turn over. If that's the case, Blissey is one of the best dust investments, even when taking attacking Pokemon into account.

There's no reason to boost a defender if the decay is gonna kill him anyway. In that case, better let it be a Chansey and power her up. My new goal is to get a 100% Chansey to level 40.