Hi Cherbhy,
I'm also in Maryland and was considering similar options (used 2016 or 2017 GTI SE vs new 2018 GTI SE), so maybe my two cents will be helpful for you. Earlier this month, I purchased a new 2018 GTI SE 6MT with leather for $28,463.90 OTD (the sale price was $26,399.11).
The price of a low-mileage 2017 GTI SE 6MT from Carmax was about $27,647 OTD ($24,097 sticker price, plus another ~$1500 for an extended service plan, and $2,050 in TTL). I know that Carmax prices are higher than average, but having worked there I feel reasonably comfortable with their inspection process, vs. some random dealer claiming they looked the car over. In either case, I would have taken the car to an independent mechanic for a pre-purchase inspection, so that's more time/money.
It was absolutely worth to me to pay an extra $816.90 to get a brand new car with a longer warranty (the Carmax one lasts five years from the date of purchase regardless of how much manufacturer's warranty is remaining), and also have the peace of mind that my GTI hadn't been abused by a previous driver, test drives notwithstanding. I'm not an audiophile, so the absence of the Fender Audio isn't a big deal for me. Also, I'm in love with my GTI's Dark Iron Blue paint.
Hope this helps, and good luck with the GTI shopping!