Have you thought of something like this. I know I would pay extra for this for my in-laws...

In all seriousness, I generally think in-law suites are very valuable to anyone who has that requirement and worthless for everyone else. Since less people have that particular requirement I think a different use would be better.

Also, any additional sales value you could get from putting in a kitchenette is probably less than the cost to put in the kitchenette. With plumbing and electrical work it often becomes a bigger cost than a return. If you don't need it for your family I would avoid doing it.

Just chatting here: if one lives in Hilton Head full time, are in-laws still alive?

I picture your location as more of a retirement/VISITING friends and relatives area.

Based on my (unsubstantiated) comments, I would bet a great guest suite would add more money to your home..designed for multiple guest:

Mammoth Cabin - David B. Smith Architect · More Info

You could do a guest suite but the buncknroom could have a small sink and a small fridge. Almost a bar set up so that if in the future someone wants to add in a small kitchenette, the plumbing is there.

You can plumb in a sink and put in a little under-the counter fridge with "coffee corner". When people visit, they often have morning routines that they like to keep. That includes a hot beverage in their "uncivilized" bed clothes (assuming they wear something to bed). They like to have a moment or two to themselves where they can stare at the wall and have a little think. A coffee station with little fridge (to hold milk, yogurt, drinks, etc) and a sink would be a great little addition without much cost.

The en-suite means they don't have to wander around at night...etc. In a retirement community/area, there should be plenty of people who have friends and family over for medium length stays. A little set-up like this would probably go over very well for future buyers.

I would prefer to see a little sofa/soft seating area rather than an eat-in kitchenette. A comfortable hide-a-bed could be used so that a few extra bodies could be accommodated should the need arise. It allows your guests a personal space to unwind before bed or escape to when they feel like reading is more their speed then a social gathering.

Just a thought.

Check with local code to see what you can add before the city would see a presumably forbidden "extra rentable apartment". Sink but no hot plate, for example. If you do choose to put in a sink, fridge and microwave combination, it will look much better if it is all behind closed doors in a high quality cabinet, like a five star hotel. Think Italian espresso maker, not Mr. Coffee.