Well, depends on you but yes, that should be OK. ssh or scp is meant for very good security, you mostly don't need it just for transferring files. WPA is already encrypted so it is almost like on wired network. If you don't regulary use end to end encryption for all traffic on wired network you don't need it here too.

If winscp allows it (and ssh server will accept it), turn encryption off completely, you will get something like a bit safer ftp and speed should go up.