My current cans are as follows : Fidelio X1 , A700 , MS1, HM5
My price range is : 100-300 for a new Amp or DAC
Is it worth upgrading from Fiio e10? Will get a substantial increase of sound quality doing so?
In that price range, I don't think so.
The e10 is a surprisingly competent budget dac. Your headphones aren't particularly difficult to drive, either.
You can look at the O2/ODAC, the Schiit Stack, or maybe the Matrix M-Stage HPA-2... lots of other options too, but the difference in sound quality won't be huge, but just slightly different.
I would say to keep the FiiO E10, more then enough juice to drive your current headphones.
Sell off the ATH-A700s and Brainwavz HM5s and then figure out what you could budget for new closed headphones.
Maybe Audio Technica ATH-A900Xs ($170-$190), with Hifiman Velour ear pads.($15).