If I may, the one thing I don't get is why people hammer about how great and huge and aesthetically pleasing a spawn every server needs to have to draw a million players. If you spend all your time working on a spawn but have no content to engage the players, all you're going to attract are people who log in for a day, go "oooh" and "aaah" then never come back. Right?
A great spawn, in my opinion (and it's just one person's opinion, take it for what it is), should be functional. It should have what it needs to operate the server, such as an admin shop, portals, maybe even rules signs (which I quit bothering with as most people that play know about /rules and ignore signs anyway). Our server has a fully-stocked enchanting table, repair sign with anvils and an ender chest. It functions perfectly.
What works best for retaining players is an engaging staff. If you have active admin who help players, engage them in conversation, actually build, fight and survive with them, they're going to feel engaged. Give them content! Make dungeons, mines, temples, anything you can imagine that requires interaction. Draw the player in. Give them something to shoot for. And most importantly, do your best to make sure they're having fun.
Granted, a good spawn that showcases these features is a good idea. But spending months on building a giant mountainside base seems like a waste of time, to me. I wish you luck with whatever you do, though! Maybe that's your cup of tea, and so be it, nothing wrong with that at all. I hope your server kicks butt and draws tons of players!
