In terms of music in mass, I think music should be included in every mass if possible, with the caveat that I will expand on below that any music used should be appropriate. How many references do we find in scripture (particularly the psalms) to singing praise to God and playing instruments to praise God?
I’m certainly not against hymns in mass (as opposed to just chant, although I do love chant

), and I even quite like the guitars as an accompaniment, but I think that all music should be appropriate to the mass in question, and to the stage of the mass. For example the communion hymn should be quiet and reverent, as people will be praying and or/receiving our Lord; whilst the opening and possibly the recessional should link to the readings of the mass if possible (or perhaps be a marian hymn for the recessional).
There are some beatiful guitar-accompanied hymns about, that wouldn’t sound right on an organ - I don’t think these should be excluded just on the grounds they are not played on an organ - there was a time when church’s didn’t have organs, and the best they had was stringed instruments.
What I do object to is the use of ‘inappropriate music’ as a way of making the mass more interesting - this is an oft-cited reason for having jazz-y music in masses aimed at young people (this ‘shine, Jesus, shine’ nonsense). If people knew and appreciated what the mass was about then we wouldn’t need to ‘jazz it up’ in any way.
All the best
Martin