One of the highlights of all D&D games I've ever played was
Finally levelling to the point I could cast 7th level spells, while the party was trapped on some awful demiplane where strange creatures were coming out of cracks in reality and just beating us to shreds.
Learning Mordenkanen's Magnificent Mansion.
Casting it so the party had some where to go rest and escape.
Taking the party on a tour of the mansion and getting super prissy about it. "Here's the kitchen. Here's the living room, no feet on the couch! The guest rooms all have private bathrooms, everybody better wash up, and send your dirty clothes to be laundered before you touch ANY furniture!"
That game continued to epic level and that character (who I had played starting from first level over the course of YEARS) created this spell using the 3.5 Epic Spell development rules. It is the best spell ever.
I think, the first casting of MMM always needs a dedicated scene where the rest of the party get to explore what the wizard has made for them. It's a massive opportunity for creativity with the players, and as a DM you can just take a load off and let the wizard player run the session for a while, explaining all the cool things they incorporated.
The first time I cast MMM in 5e, it was with my pyrophobic gnome librarian wizard, Neff. She build a special room for each member of the party to cater to their needs, and I built a map for it (we were on VTT)
That's awesome. I love the attention to detail for each party member (which is exactly what we would expect from you). I bet there's a story behind the dragon skull and the piano. I wish I still had my mansion maps from that epic game (it was about ten years ago).
(Real reason) - The rest of the party have a lot of credibility and renown in Waterdeep, due to having done quite a lot of very overt acts of heroism. They're recognized by the Lord Protector as heroes of the city, and they are widely known to be powerful adventurers.
Razira joined the party later and, while Konsi knows she's a big damn hero, nobody else seems to know this or view Razira as being that important. Konsi's constantly looking for opportunities to have Razira perform impressive heroic feats (like catching a falling person out of the sky) in public, so she gets a reputation that matches how awesome she is.
I legitimately think it'd be cool if the base sending spell had "at higher levels, you can send an extra pair of messages in the conversation for each level above level 3"
also, like, yeah all the time. One day I'll be able to bust out my lumberjack wizard who just runs a protector tree + shape wood + shrink item factory, but alas I am for now relegated to my hedge hogman breaker's quest for the 7 forbidden dances.