Yes it has been broken almost 2 weeks now, it surprises me it took you this long to figure it out lol. On a side note, sending low level alts to farm towers seems to be broken also and they don't add much to crystal buildup.
Tower farming for crystals work just fine. We have one alt in our guild that can consistently farm 3-4k crystals each siege.
You might be the exception then cause to me it hasn't worked. I think someone else on Reni posted something similar, that sending lowbies to towers didn't make any difference at all. Perhaps I could be wrong and that part was fixed on the Server Maintenance on tuesday but who knows.
My guild has tested it once we found out extractors were broke, then again after the last reset. It's always worked just like it has previous the the extractors not working. Your case is the first I've heard of it not working for players. Also tested it on my own alt guild with a level 1 toon, with the crystal extraction buffs he can pull close to 5k crystals during an hour long siege. You are using crystal extraction buffs, right?