You can not convert the transmission itself to an automatic. But you can get an automatic and put it in, although there are other things that may affect it such as that your computer is programmmed for a manual. You would have to buy the brake pedal assembly, you get it from a junkyard. The brake pedal assembly has the clutch pedal attached to it in the manual and the automatic don't. I am talking about the bracket that holds the pedals. You could have some minor complication with a shift linkage.
Why is it you would rather have an automatic? If it is an EVO I would think you would like a stick.
Yes, if it's worth it if you have a lot into your car or it's a rare car then its worth it. I did it to my civic and it cost me about $2500. I didnt do anything I had a shop do it because I didnt want to mess anything up. I really like it. They had to cut a hole for the clutch and do some other work but all in all I really feel a difference in power and in performance.
Automatic Transmissions can be made so that it only changes gears by moving the shifter. The best of both worlds no clutch but it only changes when you decide! I have been in autos that have had super-chargers added it's been done because the auto doesn't change properly. Think about it.
It is rarely practical to convert on a late model vehicle as the electronic fuel and ignition systems are different between a manual and an automatic transmission.
Kits are available for many cars and trucks to change the shift characteristics of automatics for more "racey" behavior. Torque converters are available that have different stall speeds from stock. Changing from a manual to an automatic would not be considered of value by most buyers, so unless you plan on keeping the car until it is worn out, you should consider that you will greatly reduce the car's resale value both by doing an amateur conversion and from going from manual to auto.
Depending on the application, it could be worth it. When you switch from, say, a four speed auto to a five speed manual, you will see power increases due to the change in gear ratio. If you race your car, you may see a decrease in your ET unless you're really good at power shifting. Contrary to popular belief, you CAN shift a MANUAL tranny WITHOUT the clutch. You really only need the clutch to get you into 1st gear. There's alot involved in the conversion; pedals, cables, quadrants and linkages, exhaust clearance, radiator(some models), tranny computer and harnesses, upper and lower shifter boots, and theres always the question, will the shifter line up with the hole in the tranny hump.