Vagcom should show missfires, but when I had my problem it didnt log one until it really started missing - I couldnt get it to do it all the time only at higher revs in 4th/5th.
If you can get it to log a fault you can swap the coilpacks round to see if the fault follows.
Most the time my car would run completely fine, just did this every so often over a few months.
Set of plugs would set you back around £25 I think, a coilpack is again around the £25 - each mind you.
I would recommend swapping the plugs every 10k in a remapped car - preventative maintenance.