Cecilia is the "bonus room" upstairs with closet and size sufficient to be a bed room? It sounds as if the first floor "master is a true master with closet and private bath. Is this home already one of the most expensive in neighborhood or biggest? True of all improvement considerations, these are extremely important factors. I find for example while pools may be wanted (in Fl), as many people in NJ dont want as do. (terrible investments) That gets you to the quality of life issues that arent so easy to quantify. If the house has the location you want,is in a condition you like and is priced so that you can stay with in your budget after making changes (and will not be a white elephant), go for it. At the right price any house will be a good investment.
Last word of advice though, living through construction can be vary stressfull and well beyond the cost expected.

A second master suite is not a feature normally sought after by potential buyers. They are most interested in the floor plan(split is good), square footage, location, garage size, pool, condition etc.

Don't expect that a double master suite is going to bring any great rewards.

Hi Cecilia, Adding a second floor master will make the home more attractive to families with young children, so as you point out, the parents can be on the same floor as the children. If you do it, I would suggest that you retain the first floor bedroom so that it can be reconverted down the road when/if you sell. Many buyers I am working with value the first floor bedroom - but not a first floor master - for aging parents or nannies, and having a full bath on that floor makes it all work.

Hope that helps. Basking Ridge is among the communities I service in Somerset County - please do not hesitate to reach out to me if I can be of assistance.

Thank you very much for your responses, they are very helpful. We were thinking of changing some "bonus space" to a master suite so no rooms will be sacrifice but you may be right, it won't add to the value much. The house is advertising 5 bedroom at the moment when it really is a 4 bedroom plus this bonus room. If we change it to a true 5 bedroom by changing the bonus room to a master suite we were hoping that will have some return of the investment, but sounds like this is not worth the effort.

Aloha Cecilia,

Adding a second master will most likely NOT increase the appraised value of the home and you will find it hard to recoup the cost, especially if you loose a bedroom in the process. Good luck.

A great question Cecilia,
No easy answer though. Variables include neighborhood, cost of second master, it's potential for other use... I currently have a home in West Windsor where sellers invested over $260K on a second master on the first floor with sauna, steam shower,additional laundry area, HVAC,second office... and while priced about $100K over house across the street (smaller home with less landscaping, no addition and backing cemetary), no offers yet.The biggest benefit of this will be to those buyers with extended family or aupaire needs. (or lastly the long term buyer who plans to stay many years where their own needs may change.)
If all else works for you and the addition can be made affordably (so you are not too far above the norm)do it. Price as I said varies greatly.