Here is what you can do to get the best representation of the concert you have recorded.
1) Get the best seat you can to record from.
a) If it is intrumenetal try recording from the stage
b) If it is a vocal group you will need to be a few rows back to get the P.A. in the mix for vocals. However, I have also had good results placing my mics above the monitor on stage to fill in the vocals.
2) Try running an audience and soundboard mix, which means that you will need to buy a 4 track, 2 channel mixer.
3) Run Split Omni's and ORTF's and mix.
4) Get a 16 track, multi track recorder and use 14 channels for direct intruments and 2 channels for your stereo Audience blend. Back home mix everything to your ear is content. (I know this is not feasable but it is a great one of the better ways to get the recording you want.)
After the show listen back on a very good full range system that gets down to at least 25-30 hrtz and 18 to 20 khrtz. that is set up properly in a good listening room. I would not use headphones to master since they have limitations that are only apparent when listening back over speakers. If you feel that there are some short comings with your recording then by all means try to fix or improve your recording by mastering it. BTW, Mastering usually means preparing the raw tracks for final replication. In some cases it may be just editing, fading in/out and in others it means expanding the soundstage via M/S or an expander, noise reduction, EQing, fixing balance, compression, adding reverb, etc, etc..
Remember though, that there is no free lunch. Anything you add will take away something from the recording. In the ends it up being a compromise of gives and takes. When mastering the final product it is about how it sounds to you via your ears. That is what give some engineers a great reputation, their ears and their final product.
Always save a copy of the original tracks for archival use and future re-mastering.