Look at Kenya, stay on the beach for 3 days and do a mini safari for 4 days.
damn your eyes, Archie. I was going to suggest almost exactly that. The only thing I'd add isOrient Express Company travel from London via Paris to Venice every week, then 3 days in Venice with private launch from station to hotel on Grand Canal and private launch to Murano Glass Factory visit, travel on first class train to Florence then 3 days there, private limousine to Pisa Airport flying back to London... or you could get Orient Express back home.
We did that for a lot less than £2000 each including spending money for our 25th wedding anniversary though that was 4 years ago... it was fantastic!!
Rather than exotic in destination, how about memorable in activity? I don't mean a week's pottery classes in Stoke, but something you wouldn't normally do, in a pleasant setting. Learn to windsurf/dive/hang-glide/whatever. Paint. Yoga. Hot rocks...Myself and my OH both turn 50 next year and we've decided to treat ourselves to an exotic holiday rather than go down the party / presents route.

Ilkeston. They've got a rec and a burger van and some other stuff.
a person can go off a person..............I'll second the Mauritius suggestion. Funnily enough, I am in Mauritius right now, albeit for work not a holday, and it is a very nice place indeed.