I wouldn't trust a used car dealership to suggest the best wheel/tire package. Unless you know what you want, I wouldn't even approach a dealership. You need to indicate what you are looking for in a wheel/tire package first. I wouldn't go into this without a good understanding of what you want.
Looking at what you have
205/40r17 -
205 is wide, & 165-185 are better (don't hear of rubbing issues).
40 is low profile (rougher ride), & 55-65 aspect ratio would be better.
17" rims are quite large, & 14-15" would be better.
Your rims also appear to be wide, but that's hard to tell in a pic.
I wouldn't go over 6" wide rims for a Mirage, & 5" - 5.5" may be better.
5" wide rims are recommended for 155-185 tires (these are not an easy aftermarket option to find, however).
5.5" wide rims are recommended for 165-195 tires
6" wide rims are recommended for 175-205 tires
Personally, I'd prefer 4.5-5.5" wide rims for a Mirage, but others do use 6" wide rims.
14" rims & matching tires sizes
165/65r14 (22.4" diameter) are factory size tires, but
175/65r14 (23" diameter) tires would give you more tire options. These are the two most commonly used 14" tire sizes used by Mirage owners.
15" rims & matching tire sizes
175/55r15 (22.6" diameter) are factory size tires, but
185/55r15 (23" diameter) tires would give you more tire options. These are probably the two most commonly used 15" tire sizes used by Mirage owners.
Aftermarket small rims are not as common/popular. You will have fewer choices/options than someone shopping for Corvette rims.
14" wheels may give you a better ride (higher profile tire)
15" wheels may give you better handling (lower profile tire)
The difference between these two wouldn't be that great, however.
I would shop on-line before approaching a local tire shop or dealer. Find something you like first, & see how close they can match that along with price.
Example of shopping on line for
14-15" rims that are
5-5.5" wide -
https://www.fitmentindustries.com/st...4x3.94%2C4x100
There are others like tirerack.com & discounttire.com. Just search for rims that fit your car.
Example of shopping for
165/65r14 tires -
https://simpletire.com/catalog?width...rice&order=asc
Example of shopping for
175/65r14 tires -
https://simpletire.com/catalog?resul...m=14&zip=53581
Example of shopping for
175/55r15 tires -
https://simpletire.com/catalog?resul...m=15&zip=53581
Example of shopping for
185/55r15 tires -
https://simpletire.com/catalog?resul...m=15&zip=53581
These are examples. I used the same vendor to show the difference in selection when looking at different sizes. I would check out tirerack.com, discounttire.com, tires-easy.com, walmart.com, etc..... when tire shopping. Then I would see what my local tire shop can do for me. It's not a crime to be informed when shopping for something.