Fair question.
1 I hate aftermarket decks, they are too complicated. I know sounds lame, but I like the fact that I can figure out and use every feature on these decks with out needing a book to figure them out.
2 I am a purist, so I will only do mods that look stock, or are not obvious. Now speakers, I would usually be ok with changing out, but I actually think that the JBL stuff sounds pretty decent, and for their time were actually fairly well constructed speakers (sub is iffy, but is 20 years old, so....) and since I am not looking to win any car audio competitions it's fine by me.
3. It's kinda fun to see what you can make out of junkyard parts, I spent alot less on these parts all together, than on one set of aftermarket speakers for the front doors or back seat. I think the eq and speakers was around $20-25 bucks. I would have to go check the receit.