i was about to say a few weeks ago..but it was a friend who gave me an invite D: i think it's been over a month now?
Not sure but I think it's been close to three weeks. I am a regular but never have had less than 6-8 and I just realized I am on my last one. :(
I'm pretty sure the last time I got one was in the middle of Vesnali and I know it had to have been weeks before I saw that one. Haven't seen one since.

Last month some time. Seems right after changes were made to the random events I stopped getting any invites.
[flower=jersey]
“Justice will not be served until those who are unaffected are as outraged as those who are.” - Benjamin Franklin
"Woe to those who make unjust laws, to those who issue oppressive decrees, to deprive the poor of their rights and withhold justice from the oppressed of my people, making widows their prey and robbing the orphan." - Isaiah 10:1-2
its been like a month and ive been spending a couple hours each night on the site. i think they have definitely slowed down. i hope they change it because like you said the price has gone up so much in shops its not worth buying one. its cheaper just to buy the items from other users than buy an invite and then the item.
Was this made much less common recently? If so, why?
I actually made it more common when I released the Giselle thrift rat set. :) and I adjust the rates for different random events when we feel the need to. Generally around the time we do a new set, we make the random even more common for a while.
I got one last night, almost immediately after using my previous invite, which was odd o.O
i think it's been weeks now.. which is strange. i was getting them fairly often.
the last i got one was some weeks before (not after!) the Bumbus set release but i got two in a row within hours then. so its like being on period basically, it pops up for a little while and disappears for so long that you think prices will get pregnant... T.T

I think the last one I got was during Vesnali, but it'd been a long time before that. I've always felt like I had pretty terrible luck with them.
I got one yesterday and one I think a weekish ago.. But I hadn't gotten any in a fewish months before that.
I think I got one last weekend or some time within the past week, because I bought something recently, but they are definitely far from common. If I'm lucky, I get 3-4 a month, which sucks.
It's been a while since I've gotten one and I spend at least two hours every day on Sunday doing all of my quests. I'm on zero right now and really wanting some invites but not willing to purchase any.
bird and bear and hare and fish give my love her fondest wish
a few days ago I think..there was one in my inventory but missed the event I guess..and my friends know not to send em to me because I don't use em, I usually give them to friends instead.
It still seems like these are much too rare. Prices are crazy.
It doesn't matter at all if you pay less or the same to buy a 'que item from a usershop instead of from Esmerelda. In the end, you still get the item you wanted. If you didn't want it, don't buy it.
I think the price of Invitations is about right, considering that there's been a huge chunk of retirements and new sets to collect and they're still readable.
Me, I'm still getting more of them than I can spend at the Subeautique. I never sell mine.