I have a new idea that, in my opinion, addresses the issue of both "getting the butts in the seats" and giving current, long time, players the option of keeping what they have without significant extra monetary input.
Introductory or Addon subscription:
$7.95/mo
1 plot
1 character slot
3 con slots per imperial con
1 concurrent login
Standard subscription:
$12.95/mo
1 plot
5 character slots
15 con slots per imperial con (a small increase)
1 concurrent login
Subs would stack in any combination, so you could have 1 standard and 1 intro/addon or 2 standard or, heck, 5 standard if you want!
Then offer the ability to purchase the subs, and combinations in 3, 6, and 12 month increments. Make sure to discount the 6 and 12 month increments, say $1/month per sub for the 6 month and $2/month per sub for the 12 month. So, for instance, having 1 standard and 1 addon would cost you $202.80 for the year ($16.90/mo) or $113.40 for six months ($18.90/mo) or $20.90/mo on a monthly.
I think this offers both simplicity (only 2 subscription options) and customizability since you can combine them in whatever manner you want. This also doesn't raise the price at all for those who want to keep their current, $12.95/mo, subscription and not lose any features.