Is a 7 hour layover enough time to go the city and see the Shanghai tower?

Yes, taking Maglev and metro line 2 is the fastest way except for the taxi. The traveling time is about 2 hours for round trip from the airport to the SH Tower. And you need to reserve about 2 hours at least for the transfer to your next flight. So you have 2-3 hours for sightseeing.