Many advantages to the G1 as either a first or second phone:
- It is usually the most affordable Android Phone in various auction sites
- Rugged dependibility
- Can't discount the "chic cool" of owning the VERY FIRST Android phone
- Even if you purchase a damaged one, most parts (LCD Screens, entire cases, keyboards, USB ports, speakers, trackball, and digitizers to name a few) are comparitively cheap, and fairly easy to replace
- It works VERY WELL in stock form. And rooting/customizing/modding is fairly easy IF YOU READ UP FIRST (As a aside, it's also easy to "brick" if you DON'T READ AND FOLLOW DIRECTIONS)
- Running custom ROMs is real easy. I tend to have 5-6 on my SDCard at any one time, and switch between them at random times (For this, you may want it as a "backup phone", because while you're messing with it in Fastboot and Recovery, you ain't gonna get any phone calls and texts)
I use my G1 as my "main". I bought it for $30 on eBay (was an accidental purchase...lol...Forgot I even bid on it), and except for a small crack on the 'chin', and a "bulged battery, it was perfect. After buying a HUGE battery/back cover for it (about $15), I get 2+ days of use. That's with WiFi, 3G, apps running like mad, and using 4 GB of data last month.
In conclusion, you can't really go wrong with it, as long as you buy a working one. If it isn't working, you MIGHT be able to get it back to life.