Which new ReadyNAS

I have a ReadyNAS NVX Business Edition [X-RAID2] with 4 x 512GB drives in X-RAID2 which has provided sterling service since 2009. I use it as a centralised file server and also backup to

1. A seperate disk on one PC, which is always on
2. 2x USB disks (one of which I take offsite, in rotation, every month)
3. ReadyNAS Vault (a small amount of the most important files only)

I keep addings photos, and my daughter will be getting a GoPro for Christmas so will start to add video, but as you can see, capacity is not really an issue. I am only at 56% of 1353GB used.

Very rarely I use a DLNA server to stream photos/music to one of the TVs in the house, or even a movie (that is encoded as an mp4 in SD resolution)

I would like:

1. Dropbox like access to my files when away from home - especially those on home shares (which ReadyNAS remote could not manage)
2. Faster backup (a full USB backup is so slooooooooooow)
3. The footprint to remain the same, or smaller (actually, the height is more important)
4. It to be reasonably quiet

I was considering buying a new product and then using the old ReadyNAS as a backup, with replicate (I have a licence). I could locate the old product in a seperate building.

What product should I buy?