Hi Mats,
The easiest way to import a lot of files from a nested directory structure is to navigate to the parent directory and use the search function in the open file window:
You still have to search for each file extension separately (.slg, .sl2 etc) but you will get a list of all files matching your search pattern in the current and all sub-folders, which you can then select for import.
You didn't dream the tide offset; a single water level offset value to be applied to the current import batch of tracks, coming soon :)
Matt