Just keep trying different branches until you find one that will allow it. As Tod mentioned, it's entirely up to the branch manager. Took me several tries (even on a long stay visa) to finally open one.
The law is you give way to the vehicles to the right (i.e. vehicles in the roundabout). But Thai's either don't know this rule (if they even have a license) or care to ignore it. I find if they're going 'straight' they just go regardless of whether you're in the roundabout or not. So keep these in mind:
1) you're the foreigner so regardless whether you're in the legal right or not, you're in the wrong.
2) approach any roundabout like it's a regular road intersection with no stop signs or traffic lights.
Yeah... I would go that route. It only took me about 30 minutes to extend my visa at CM immigration recently. And, I would be worried they would say "your visa expired, you have to start over" if you waited for the amnesty to be over.
Every immigration office does things their own way. You have to talk to your local imm office if you're unsure of something.
Now is the time to do your extension because the offices are very quiet (I was in and out in 45 minutes). And, nobody knows what will happen after the visa amnesty ends so... just do it so you don't regret it. I can see them saying you have to start all over again if you don't extend your current visa before expiration date.
I just did mine last week here in Chiang Mai. You can do it up to 45 days before expiration. I am Non-O so no insurance needed and 800K in bank. Things I needed:
1. Back statement for 1 year (took 1 week to get from BKK Bank) (picked up on Wednesday)
2. Letter from bank confirming account and balance (picked up on Wednesday)
3. Photocopy of all pages of passport + TM30. (sign all pages)
4. Photocopy of all pages of bank book updated the day you go to Imm (should have a B/F entry on the day you go to Imm. I did Thursday morning before going to Imm) (sign all pages)
5. Photo
6. The 4 forms they have at the counter for you to fill out
many Thai consulates have different requirements so contact the Thai consulate in your area and get the requirements for the six month multi entry tourist visa. It's the only way to know for sure. As Tod mentioned, some require proof of funds, others (for example Toronto) do not. Contact the consulate.