That hard drive is killing everything more than you think. Trust me. My 11' MBA is the same computer as yours except the "HD". I have alot less space but it is a SSD. I have zero trouble having multiple apps open. Even with 4 or 5 apps open, I can open another with little hesitation. I edit video and photos on this thing in no time compared to my mini that I had. I honestly would NEVER own a standard HD ever again. I wouldnt even bother with a fusion drive either. Its all flash storage or nothing for me. It really makes the computer thatm uch faster. Not to mention it wakes up from sleep mode nearly as instantly as an ipad.
I put an SSD in my windows laptop, and have to agree that full ssd just spoils me for anything else. That said, it just isn't feasible to NEVER go to just a ssd like you said, for most people anyway. I have many gigabytes of music, and several hundred gigabytes of photos. So 1TB is bare minimum for me right now, plus I need to back all that up. Ideally I'd like 3 TB for backups, but right now have 2TB. Considering that 1TB flash drives cost in the mid hundreds of dollars, it just makes no sense right now to be 100% ssd. having 2 drives, an ssd for the OS and a traditional for most other files, is ideal. The fusion drive seems to hit the sweet spot between having a single drive and price and speed.