As Mike says, it depends where you are starting from.
I used to work in Holland for 1 week each month and as I lived in Milton Keynes used the Dover /Calais route and drove up to Noordwijk.
For the sea, I would recommend Katwijk or Noordwijk but beware the wind which can be cold off the Noth Sea. Noordwijkerhout has a good beach but would probably not be suitable for your wife as it is beyond some dunes. Leiden and Madurodam (sp!)are both well worth a visit and of course you have already mentioned Amsterdam and Delft.
I would also recommend that you visit Northern Holland, crossing the Issjelmeer (There was atime when I could spell these!).
I'm sure that you will enjoy the country especially as there are no language problems.
Delftse Hout is an excellent site which is situated within 20 minutes walk of Delft.
It is a large site with an area set aside for static's owned by Dutch residents and also several static's for Eurocamp (they also have tents erected there)
Pitches are level and the ones for vans and motorhomes are semi-hardstanding, 2 or 3 units with plenty of space between on pitches which are separated by hedges. There is ample space for tents too.
The site has a good information point, a well stocked shop a decent size pool and kiddies pool, play area etc
A restaurant, take away and bar with good food and friendly service. There is ample entertainment laid on for children too. Most important is that it is quiet after 10pm. The toilets and showers (including disabled) are first class and thoroughly cleaned every day. Water points are ample and rubbish is deposited into shutes which take it to underground containers. There is a chemical disposal point and refill point for water tanks.
Loads to see and do from this site, a lake closeby with a small beach area, loads of interesting walks and of course the inimitable cycle paths. Wildlife abounds on site with rabbits, ducks and moorhens all calling round for breakfast!! The rabbits love McVities wholemeal!
Catch the bus into Delft (better than trying to find a parking space) Two markets weekly, a large one Thursdays where you can taste all the cheeses etc., and a smaller one of Saturdays which also has a variety of 'bric a brac' stalls. Plenty of places to eat in Delft but we recommend Cafe de Waag, the food here is excellent and inexpensive. Some of the corner cafes are good also but you can get quite 'high' depending on which one you frequent and that applies to non smokers as well!!
Visits to Rotterdam, Amsterdam, Den Haag and Scheveningen are a must whether by your own transport or by public, if you are using your own transport then don't forget Kinderdijk and the windmills - its time stood still!