I also prefer to purchase balls with a similar span to mine for a couple reasons:
1. I can use a bigger slug to fix the span to mine.
2. Doing so will not affect the value of the ball (since plugging a ball can lower the resale value anywhere from 5 to 20 bucks).
3. I also buy balls just to try different reactions. I don't want to plug a ball just to see if I will like an early roll or skid/snap reaction.
4. I have some friends or regular business partners with my span and they may want the ball if I don't like it. This way they can try it.
I don't buy balls with my span to save cash, but to ensure that the ball remains at top quality for either me or whoever I sell or trade the ball.
I think spans should be posted because I send about 5 messages a week asking people about spans.
ALSO, think that drill patterns should be posted. I hate buying an aggressive ball which is drilled non-aggressive. It defeats the purpose of the ball. I then either have to deal with a reaction I don't like, plug the ball, or get rid of it when I really wanted it.
I think that these should be included in all post:
Name of ball (DUH!!!)
Weight (DUH!!!)
Span (Saves the trouble of asking)
Drill Pattern (Couldn't hurt, maybe even the reaction given)
Condition & Any noticable marks (It's only courtesy)
Grips or Slug?(It affects the span and some people must have these)
Just my opinion. Man I wrote a lot!!! lol