Whatever be said of the aesthetics, the refit we see is actually among the most realistic in Star Trek. That's what's really
done with ships that no longer can serve on their original merit: new gear is bolted on, old abilities are lost forever, and mission flexibility is given up for the ability to mount one decisive piece of hardware that no other, self-respecting ship type will agree to carry.
The triple-naceller most reminds me of the British monitors of the World Wars, except that this time it's the old spaceframe that's carried over and the weaponry that's modified (whereas those British ships had high tech supergun turrets installed on first one generation, then another of shallow-draught, bargain-basement hulls). Probably Starfleet saw the one purpose this giant but obsolete ship could still fulfill: the carrying of the clumsy, outsize phaser lance.