The downside with using Glyph this way is that--if I'm reading the spell correctly--you need to cast it at the level of the spell you're storing in it, which means you need two slots of that level: one for the Glyph spell, one for the spell you're storing in it. That seems to mean you can't store anything cast at higher level than 7th in it.
Yes... That's why I ruled out simply Gating the meteor-happy spellcaster right over a big X painted on the floor, though there might be somewhere in the rule a solution to cast 2 9th-level spells on the same day. Creating a scroll would make it prohibitively expensive if it was allowed, the rules specifies that the triggered spell must be cast as part of the casting, so a Simulacrum can't stand ready to cast the spell...
(BTW, when DM'ing normally, I'd probably veto half of the 10 methods to locate the kille (or use them as opportunity for a side quest), but I'd be inclined to allow the glyph of warding trick... if only because I'd feel no qualm about using it against the players.