do you own vehicle out right? do math on annual car payments and compare with annual maintainence bill. ask tech. if there are other things that may go in the near future. consider needs and wants and whether or not they balance out. good luck.
another thing you may want to consider is warranty. your warranty is obviously up on your current ride. so if you decide to cut your losses and move on to a new ride, you may want to consider taking care of whatever maintenance issues you can on your own first. anything you feel confident enough to handle. get the ride detailed right before you bring it for trade. paying extra for a ride with a fresh warranty may be worth the trade off.
on the other hand emissions is mainly an ignition and exhaust issue. there are additives(ethanol treatment) you can add to fuel periodically that will clean current fuel system and cat. conv. to enhance burn and exhaust. a fresh set of performance grade plugs and ignition coils as well as switching stock air filter for high air flow type will also help promote cleaner burn and fuel efficiency. adding oil stabilizer during oil change will also help reduce emissions and restore performance. a new stainless steal type exhaust system may run up to around $1,000.00(with a fair exhaust tech.) but will last you 10 yrs. plus.
i hope this helps in your decision. again, good luck.