Couple points to consider.
First, a spare rifle is incredibly useful, especially if you shoot a lot or do classes. If you primary fails, just grab the backup, and keep on running.
Second, consider the current political climate. Right now, parts and rifles are easy to get. But come November 9th, depending on the result, things may be a bit tougher. I've been on here since 2003, I've been a shooter much longer than that. I've seen several different panic periods, and while all are a little different, there are certain patterns;
Parts to upgrade your rifle are plentiful. Stocks, handguards (rails), grips, etc are plentiful and easy to get and don't really go up in price much, if at all.
Parts that are essential to the function of the rifle, such as BCGs, Triggers, LPK's, etc tend to dry up and go up in price pretty significantly. 50-150%.
Parts that define the rifle, such as Lowers, complete uppers and complete rifles are extremely tough to source, and the prices go way up. Sometimes 200-300%. 2 weeks after Sandy Hook, I had a co-worker offer to purchase a basic carbine and 10 mags from me for $6k. I paid less than $800 for that carbine. Sadly, I only had 2, so I turned him down.
So consider what you have, and what you would like to have. Plan and purchase accordingly.