Is it a good idea to get my neighbor to sell too?

I would only consider it if both apartment need Reno and the combo layout works well. The size premium per sq ft is not very large currently. A combo apt will get a gut Reno discount on top.

just sell yours if you can before dreaming something else

Maybe your neighbor would like to buy your place and combine it with his, so he can get the space he wants to move back in. Worth having a chat with him to see if he'd be interested in buying and you could do a direct deal with him. Is there a history in your co-op of combinations of similar units that might help persuade him, or another buyer?

Agreed. It only makes sense if (i) the combo is cohesive, (ii) will enhance the overall value of both units, and (iii) the maintenance will not be too high relative to the market of what type of apartment the combo could yield. Awkward combos will diminish the value of each unit and may cause each unit to sell at a discount relative to what they could have realized on the market independently.

If a combo of these two lines (or two comparable units) has sold recently in your building, you should have a pretty good idea of what the market thinks of the layout (or potential layout).

Dan Gotlieb
Digs Realty Group
https://digsrealtynyc.com/

In the current market it's not the same as it used to be. Back in time the impetus behind so many combinations (many of which didn't really work out that well) was the lack of inventory in larger apartments.

But looking at UD existing resale chart you've got 1,663 1 BRs and 1,470 3+ BRs currently on the market. So with plenty of larger units available the number of people willing to undertake large projects just to end up with an inferior layout has wanted.
All that said, it still depends on your particular situation and what the apartments of each size are currently trading for in your particular building. One example I could think of is if one of the units had a nice terrace, combining units could still make sense .

byq

BTW there are a few recent examples of people buying poorly combined apartments, de-combining them, and selling off the pieces at a profit.

why don't you buy your neighbor's place and combine it, then you can sell it for huge profit

Have you put together a floor plan for your vision for a combined apartment that would appeal to a buyer?