I really ummed and ahhed but in the end we decided not to find out. Some of our thought processes are below, but none of these were really strong enough on their own to sway us. In the end we just didn't quite feel strongly enough to find out, so it seemed easier to take the passive option of not finding out. Our 20 week scan was on Friday btw.
Agree that it is the same surprise for us whenever we find out; however for other people (well, our parents) I think it'd be a better surprise for them to find out when the baby arrives. (we could never keep it a secret if we knew!)
Like you, it won't really change anything we will buy, although I have seen a couple of lovely handmade dresses... Anyway I like the challenge of finding nice unisex things (NOT beige and grey...), and it means the stuff we buy for DC1 can be used for other kids regardless. Also it stops people buying lots of frilly pink stuff or boring khaki/navy stuff.
I can see the sense in finding out for DC2 for planning purposes; so we thought if we find out for DC2, we shouldn't for DC1 so that we can experience both ways!!
We have 95% decided on names for each sex, and if we knew the sex, I worry that I'd start calling it by the 'right' name and thus potentially spoil another surprise for our parents!
I only had a slight wobble during the scan but managed to hold out. We told the sonographer upfront we didn't want to know, and baby didn't flash his/her bits at us, so we're pretty happy!