Anybody experienced a boost on this year's 50off day?

I did a little, but was just a fragment of the previous year.

I experienced significant increase on other matkets. 3DExport is totally dead for me with 0 sales this year.
Last year I got 8 sales.
So other markets are growing rapidly, 3DExport dying.

And on those others, there's no cause for concern? No sizeable drop compared to previous years?

Do you think maybe those marketplaces differ in any way regarding offered material? (i mean overall, not your portfolio specifically)

Competition is growing everywhere so sales are dropping a little bit everywhere, but on other markets you can maintain some regular frequency of selling by publishing new models - so not dramatical drop.
I don't know what is the point/reason because I am not buyer so I don't know why this site is not so attractive for buyers like other very famous marketplaces.
For example TS has very good cataloging - search result is very good with high quality models on 1th place.
Garbage (cheap low quality models) is placed on last pages (not visible).
This is I think the key value for professional buyers that search result is not so messy.
From seller site on other markets you can opt-in or opt-out discounts or set percentage, you can use newly developed features like collections etc. The sellers forum are alive you can get advice from other users.
Or simply buyers are visiting sites with over 1 milion models available. If you are searching for some very specific model you will probably not find it here on 3DE.

3DExport just barely if ever comes up at a decent place in a non-specific "buy 3d" Google search, so that could be a reason. I've chosen the Exclusive Seller route here many years ago and i'm well nearing my 7th extra royalty percent, so i'm kinda bound to this place, no way for me to experiment with switching. But i guess finding one's niche can more or less overcome the fact that their platform may be in great marketing shape or not. If you put up distinct stuff that is also quality, by time you will find that they get direct Google links in searches, no matter exactly what platform they are on.

Yes it is also way if you have specific (unique) stuff then it should not matter on used platform. Customers must buy it where the stuff is available. Or even smaller platform with smaller competition can be advantage.

Nobody bought nothing of mine in this boost day

1 sale in the last 1 year, whatever they did they broke the site