From a fluff perspective, Sallys are the "nice guy" marines, and that's tricky in the Grimdark. Their Chapter Tactics more-or-less require Vulkan, past a reasonable point level to get that MC Melta amazingness.
So whatever supplement you'd add, you'd need to either fold Vulkan's buffs in, or make Vulkan part of it. Sallys aren't really known for their speedy movement, and 7th rewards that, so they'd need a work around for that, to make the supplement sell.
I like playing Sallys. I split my time between them and Ultras. I was actually kustomizin' some combi-weapons for some Sergeants this evening. Drop-Sallys were super popular in 5th, for the meta-crushing melta-spam, but that's gone by the wayside starting in 6th, and pretty much killed it in 7th, from a competitive standpoint. Melta's less awesome than it once was, and buffed flamers... well... let's just say that Necrons, Knights, and Wraith Constructs have little to fear.
Master Crafted close combat weapons are also less than spectacular, in the current edition. So without revamping Sallys to, say, master craft all weapon upgrades, or something, then there's not much more you can do for their existing bonuses, besides make some Chapter Specific units [Dragon Knights!
] or re-craft the fluff to support some other rules overhaul.
They aren't hated, but I don't think there's much you could do to tweak them from what they are.