We will have several hours in Dresden and Frankfurt (almost 8 hours) that we don't want to spend in the Train Station. Do either/both of the stations have "self-serve" luggage storage? We have one carry-on bag for each of the two of us. I'm hoping the storage is "self serve" so we don't have to stand in a queue when we return to the station to catch the train.
The lockers in Frankfurt that are along track 24, are easy to get to. For 2 carry-on bags, one of the lockers for 5 euro should be enough. You will need coins for the locker.
Virtually all major train stations in Germany have lockers. Look at the maps below. Lockers (Schließfächer) are shown as a box with a suitcase in it and a key. Dresden (https://cms-bahnhof.noncd-web.db.de/sites/default/files/pdf/dresdenhbfdb_vst_a4web_1.pdf): There are lockers at several places on the main floor. Some are near east exit (Ausgang - Wiener Platz, Prager Str). Frankfurt: (https://cms-bahnhof.noncd-web.db.de/sites/default/files/pdf/ffm_a4_web.pdf) In several rooms (in blue) to the north of the main exit. (Sorry for the cut-n-paste, but once again BBC has failed us)