If you need the space and it would add value in your eyes and to your usage of the unit, go ahead and buy it. If you are selling in the very near future and don't have a lot of equity, might want to do some research first.
Please feel free to contact me if I can be of help to you.

Best Regards,

Mary Ann Jarvis
Prudential Fox & Roach
Brigantine

Buy it. The numbers make sense, you can always finish it out later. 553500/1645 is 336.475. The current value is apparently 345.sq ft, so the new value would be 567525 for the whole place. Your 3500 investement would be worth $12525. Of course, your would need a door, and some labor, what about 2500? at most. So you would still be up 10,000 in a matter of days. Plus, you can always say that is an 'office space', rather than a closet upon selling, so it would certainly pay for itself.

I'd jump on it.

One way to look at it is that your condo is about $345/sq ft.
The asking price for the dead space is $78/sq ft
So, if you think it will enhance the space and the cost is not a hardship, maybe.
Are there any negatives?
Do you want a project?

Is the closet space in your unit not enough? There are many things to consider, not just the price of the space. You need to know how much finishing it would run? To be sure its useful, where is the enrty door planned? Will it increase you monthly condo fee? Many questions!