I would never suggest you buy an ATN, but with that in mind, the difference between 160 and 320 is fairly staggering. It is the difference between having blobular targets at distance and fairly discernible targets at distance.
You have to understand that in the resolution game, 320 is 4 times as much resolution than 160, and not just double? How does that work? You are dealing with a grid. For example, say you had a grid of 2x2 blocks. That covers 4 times the are of a 1x1 block. Make sense?
When you double the magnification (digital zoom) on a 320 scope, you are now looking at a 160 image. When you double the magnification of a 160 scope, you are looking at an 80 image.
I don't know the particular scopes you are talking about, but will say some companies will make their 160 scopes a much higher magnification and their images may be comparable to a 320 scope zoomed 2x (to 160 resolution). In cases like that, the benefit of the 320 resolution scope is that you get a much wider FOV at the original base level of magnification. If it is the only thermal you have and you have it on a rifle the wider FOV means not swinging your rifle around as much to scan for targets (which isn't a terrible safe practice, but is commonly done).
I have no clue what you budget is, but I assume it isn't a lot if you are looking at ATN and bottom tier scopes (we all start somewhere). You might want to consider looking at the lower end Bering Optics Hogster or AGM scopes...in 320 resolution.
Another option I would suggest is that you buy a hand scanner in thermal and go with something like a Sightmark Wraith digital night vision scope (which you can use in the daytime as well) if you are hunting open fields. If you are hunting in heavily wooded areas, I would not suggest this option. The benefit here is that you can safely scan for targets with a spotter (which tends to cost less than rifle scopes) and shoot with the night vision out to a couple hundred yards (which most folks are shooting inside 100 yards at night) and generally be safer than waving your rifle around to look for targets.
There are some folks who trust their RTZ (return to zero) mounts to work 100% of the time and take off their rifle thermal scope to scan with and then put it on the rifle to shoot. That can be done as well, if you have the right mounts. I don't know that you will find them on the low end scopes. The down side to this is if you don't remount the optic properly (which is usually in the dark and sometimes under pressure because the hogs are RIGHT THERE!), your POA may no longer coincide very well with your POI.
