Not quite.
Summer rentals for us are a steady stream of families booking for a week, requesting high chair and cot. There is still a place for bucket and spade for people who can't face taking small children through airports, delays etc. That said, we get plenty of comments afterwards appreciating the good washer/dryer and the pile of children's DVDs.
However we are lucky that the flat is not only near a good beach but also somewhere with a boyant economy with good transport links and a University, with some lovely walking country nearby. We have regular bookings from some grandparents who come down at half terms to help with child care, quite a lot of couples from May through to mid-October takng a week's break, parents installing their children in a nearby language school, house-hunters looking to buy, people on extended business trips looking for a serviced appartment etc. We even had some Bulgarians usethe flat as a base for a November walking holiday. I felt a bit sorry for them.
But even with all of this we would be better off simply letting it to local young professionals. Far less work and much cheaper. Though holiday-let agency fees are high, I begrudge them far less than normal agency fees. Holiday lets are really hard work.
The flat is also the right size, two bed two bath and nothing pretentious, and in a good location for both beach and town. Really nice properties in the area can be very expensive but without much rental premium. There is a danger of stag/hen bookings with larger properties.
It suits us, as my mother is near-by and long-term ill, and it suits us to have a base so visits can also be mini-breaks for us. Good transport means that our older teenagers can use it. And it is great that we come some way to covering our costs.
There is no guarantee that something by the sea will rise in value. In fact seaside towns have generally suffered with the switch to foreign holidays, and then by having this surplus accomodation used by benefit claimants. The summer season is very short and so there is often a lot of winter unemployment. In rural areas, second home purchases tend to depend strongly on confidence and disposable income, so the market is very volatile. If interest rates go up prices could well fall sharply. We have made capital gains, but these relate to the strength of the local economy, and these reflect rises in other economically sucessful Southern towns, not just those by the sea.
In short it can be worthwhile, but only if part of the return is your own ennjoyment of the property and if you have done your market research and costings carefully.