7" Singles

I will always buy the 12” if there is one. I only buy 7” if it’s the only way/only affordable way to get a song.

When I was a kid it's all I could afford, so I would buy them. The first record I ever bought was Elton John's Philadelphia Freedom with a picture sleeve.  I think it even had the lyrics printed on the back.  I must have played it a thousand times.  It cost me $0.99 plus tax and I wish I still had it.  
Once I bought the 45 of "Walking In Rhythm" by The Blackbyrds, and discovered that my grandmother, who despised rock music, really liked when I would play it for her.  Later in my adult years I really got into Donald Byrd (mostly while smoking pot), but it only recently occurred to me that he was the main force behind The Blackbyrds.  Funny how things come full circle.
But that was before I developed a taste for hi fidelity.  In the 80's a lot of the punk bands I liked released 45's with non-LP B-sides that made me want to collect them, so I get what you're saying about their appeal to the collectors. 
These days I've decided to focus on the music and not the collecting aspect so maybe that's why I no longer appreciate them.   

You are right about laziness with 45s when it comes to home listening, it’s more fun to play them in public with two turntables and some dacing people.

However, rough 45 versions of the songs/compositions are mostly different from the LP version and not only because it’s shorter, but most time it’s different take and different arrangements.

Most of the 45s from my collection has never been issued on LP, most of the obscure bands not even got an LPs in their discography. This is the reason i love 45s from the 50s, 60s, 70s and early 80s with Jazz, R&B, Gospel, Funk, Soul, Latin, Reggae ... music.