When you say upconverted are you refering to say a standard DVD being upted to something like 1080p??? If so then no they wont and Im not sure anything that can. Even with everything that I have seen that says it upconverts the fact of the matter is you cannot creat data that isnt there. Most gimmicks are just that, gimmicks. I have been more than just impressed I was pretty blown away but the output quality from my mini compared to my panasonic DVD player that was connected to my TV via component output. The mini has much truer color saturation as well as almost no artifacting at all.
I will tell you that I have started to move my dvd library to an external drive and play them back through PLEX and its everything I had ever dreamed of. I remember a couple years back I saw a company called Kalidascope, they are a very high end Home theater manufacturer that made a device that could catalogue and organize DVD collections up to 300 movies for 10,000.00 or 500 movies for 12k. Then you would buy their special front end box to watch them throughout your house. The front end box ran about 1500.00 or so each and you needed one on each tv. I just thought how effin cool is that and I really wanted to have something like that one day.
Well 5 years pass and now I have a mac mini that set me back 600 a 2TB drive that set me back 250 and AEBS that was 150. All said and done I am into the set up for well under a grand and it will do everything the 12,000 dollar system can do. In fact all I have to do is add Mini's to my bedroom and den and I can access my entire collection wirelessly without any issues. I actually tried it using my macbook and it worked perfectly.
My only other suggestion on top of buying an external is make sure you buy something in a raid 1 config.I probably have a couple 5 hours into moving my 30 movies over so far and when said and done it will probably take about 15-20 hours to move over my entire library. I really dont want to have to do it all over again so if one drive fails, I pop it out and put in a new drive. The system automatically rebuilds the new drive and I am back in business. Also if your the kind of guy that double raps your goods, then you could even finish your collection pop out a drive and pop in a new drive. It will rebuild the new drive and you can keep the spare drive offsite just in case of a catastrophic issue, IE power surge, fire ect.
Hope this helps