Who likes to make friends while on holiday? I can't stand it, you end up having to work round other people because they've arrange to meet you at a certain time so they can have a drink with you! My wife and I like to keep ourselves to ourselves. There is nothing worse than people thinking they can come and sit next to you and start talking to you whenever they see you just because you said hello to them once. They just ruin your holiday, just go away! Better just not to speak to anyone.
I understand what you mean - OH and I like to go away and be on our own, but we do like to be sociable, say in the bar at night - but we don't want other people bolted to our legs. We're sociable, but not matey with people.
Having said that, I am still friends with two couples I met on different holidays 20-25 years ago, but that might work because we live at opposite ends of the country :-)
Surely the answer here is to be polite but say you can't meet them for a drink as you'd planned to have a romantic evening together. This way, even if they run across you they will probably stay away from your table as it's your romantic evening.
When I attended an international conference in Adelaide (in 1986) I was hoping to make some friends who could provide me with free holiday accommodation. Unfortunately the only really good friend I made there was the UNESCO Advisor on Mathematics Education in Beirut (at the time when any westerner entering that city was likely to get an extended free 'holiday' chained to a radiator!).
I once won a weekend at Champneys. Got in conversation with a woman who spent a lot of time there as more money than sense. She then cornered me at meal times. On the last day I was determined to eat by myself. Went behind a screen that they had near the edge of the room. Breathed a sigh of relief as I began to eat until I heard the words "Oh there you are".......