Evil GM " Hmm, Low Magic=Good, High Magic=Bad? I guess it's just a matter of taste and how familiar you want your fantasy. Personally I don't like magic to overcome all obstacles - ie a magic shelter to protect from the wind, a magical ever-filling cup, a bag that provides an endless supply of provisions. Maybe that's down to the style of fantasy novel I was brought up on - I remember reading the likes of David Eddings where magic wasn't something you used everyday to overcome every slightest issue - the characters still had to find food, got wet and miserable when it rained and got lost from time to time. I guess it made the stories and characters more accessible if, despite their magic powers, awesome weapon skills, ninja-like stealth etc they still faced the same issues we could imagine ourselves facing in similar situations. Hence I've always had a fondness for the 'book-keeping' side of the game - do you have enough rations, who has the torch, does the Wizard have his spell components, is your PC carrying enough to be encumbered yet etc. And for that to work you need a relatively low magic world.
But in the context of a fantasy RPG I can see the argument for removing these fairly mundane tasks with a little magic 'faerie dust' so the PC's can concentrate on the 'fun' parts of the game - storming floating castles, defeating fierce ogres, disabling deadly traps and solving fiendish puzzles without having to slope off home every few games to get more bread and bat guano, and counting every gold piece to see if your PC can still walk under the weight of all that loot. And as soon as magic is commonplace enough to solve all the mundane issues you will normally have a high magic campaign.
As for High vs Low tech - just doesn't do it for me. I've never been a fan of Steam Power or Gunpowder in D&D, and even Techno magic leaves me cold. Never bothers me when we play 'modern' games - Call of Cthulu, Dr Who, Buffy etc, but I like my fantasy medieval so ban anything overly technical. In fact my Anval campaign was originally conceived with a bronze age level of technology, but as soon as the players started creating their PC's and wanted Plate Mail, Repeating Crossbows and the like I dropped that idea to avoid keep saying 'no' to the players."
My personal leaning is that a setting that includes magic cannot stick to medieval 'norms' of technology and therefore its application should be carefully controlled by the game system. Magic in effect becomes a replacement for science in a fantasy setting and I would expect some bizarre and incongruous combinations of inventions to exists in any world where magic was as universal as it is in the current edition of D&D.