matched inlets allow air to flow more freely and people have said they allow their cars to rev easier and feels like engine has a tad more torque..apparently one of the greatest increases with an RS for not alot of moneys. Getting mine done soon hopefully! (correct me if wrong people, just used the search function)
CDA will sound better but tbh your better with a panel filter for performance.
Your car looks in top condition though mate, but if you do have some swirls get somebody to have a go and pc'ing it. I got JD aka jamie to do it off here and he did a fantastic job on mine and i will take my 182 to him again in spring.. looks mint when done!
Matched inlets are usually done as an exchange, ie they send you the matched inlets and you send yours to them plus money, or if you have somebody local they will obv do a drive in service which is what im looking for really!