It's tough to ski around here this time of year WITHOUT a car. I live here, but coincidentally I'm flying out on April 13th... maybe we'll cross in the airport.
If you ever come earlier, I highly recommend one of the bus deals, particularly to Hochzillertal. http://www.skibusmuenchen.de/ Can't beat the price or convenience. But the last trip was this past Saturday. :(
Hochzillertal is a great option, about 1.5hrs by car/bus. But a real pain via public transportation. And the base is hard-frozen by this point, though you can still get a powder day. Hintertux is definitely still producing big powder days and big vertical... but it's a pain to get to even by car (2+ hrs). That said, it's my late/early season powder day-trip of choice. However, it's also one of the more dangerous places around here if you venture off-piste: big terrain, crevasse/slide risk, exposure.
Zugspitze is beautiful, but as mentioned the pistes aren't worth even looking at if you're beyond an intermediate. The off-piste can provide some fun short runs*, but its very weather/skier dependent. If it's skied and hasn't snowed recently it can get very re-frozen. And it's expensive for what it is, a bit of a hassle to do as a day trip, and the most interesting stuff up there can slide/get you very lost if you venture too far away. That said, it might be your only real option given your transportation limitations. And the Garmisch Classic area probably doesn't have much snow or is closed by now. And anyway, the only real accessible off-piste is in the top/back (Alpspitze) and OK, but not mind-blowing.
If you do go to Garmisch, make sure to check out the Partnachklamm hike (really cool gorge), and the Partenkirchen side of town, which is MUCH nicer and smaller than Garmisch proper and easily missed.
That, or skip skiing and make a pilgrimage to Andechs Monastery/Brewery, and make sure to order the doppelbock dunkles bier and a schweinshaxn. And if you can swing it on Sunday-- I hear it's going to be sunny finally-- swing by the Chinese Tower for one of the season's first biergarten days.
*There are actually some HUGE off-piste routes, but they're not even close to accessible without a guide or extremely knowledgeable local. And at least one variation requires a significant repel/abseil.