Is it still worth investing in a second beach house?

It depends on which area you're looking at and how much you can afford to tie up in it. Because the second home market by the sea has gotten pretty saturated in a lot of areas, prices aren't growing like they used to and the management costs - taxes, maintenance, maybe short-term rentals, I don't know - eat up a good chunk of whatever gains you'd make. If you just want it for your own vacations, that's one thing - it's a luxury, not an investment - but if you're counting on making income by renting it out, honestly the numbers often don't work out, at least not like they did 10-15 years ago.