For us gun cranks there is no need for a legitimate reason to buy a new rifle in a new cartridge.
Having said that, the .17 HMR is IMO the best small varmint rimfire round out there. It gives the standard .22 Hornet a run for its money and is actually better suited for the small varmints like sage rats, starlings, and crows. What it isn't is a good cartridge for hunting edible small game like cottontails and grey squirrels that are shot at 50 yards or less. If you are looking for a rifle for small game hunting, get a .22 LR. If you are looking for a rifle to bust small varmints like crows, starlings, turtles in your pond, small ground squirrels, etc., then the .17 HMR is the bee's knees.
What I like about the .17 HMR is that I don't have to stress about keeping track of spent cartridges while I'm dinking around. Sure, my Hornet shoots a little flatter and hits a little harder, but it's nothing to grab a box of factory .17 HMR ammo and go shoot something. No thought, no planning, no prior reloading session, no hassle, no muss, no fuss.
I'll always have a .17 HMR even though I'll keep my Hornets. Geez... all this thinking has gotten me in the mood to go shoot something!
Oh... by the way I have been able to hit critters repeatedly with a .22 LR at 300 yards and out. When you're shooting over a very thin layer of water over mud you can see your bullet splashes and figure out the correct holdover pretty quickly. That does not mean that the .17 HMR, or the Hornet, or the .223, or the .22-250, or the .308 is a much better cartridge for longer-range shooting than the lowly Long Rifle.