It's all rather academic now since, as I said in my original post, the increases in my assessment slowed down for a couple of years, and the neighbor I cited is now assessed higher than me--he's gone from $250K under mine to $100K over.
That is an odd thing of him to say you and does not jive with how the assessment system works.
You do not need to appeal your neighbours assessment, you just need to make BC Assessment aware there is an error. Nothing will change for this year but your neighbours should be closer to you next year.
I think it is worth you appealing and get a full list of comparable sales, the $250K is too far off, way too far on the surface of it. I suspect your house is likely too high and the comparable sales would show this.
I did what you suggested here--complained that the values were wrong (relatively) and although the assessor said "appeal your neighbors' assessments" my assessment increases were retarded in the next two years.
I appreciate that you seem to have a lot of faith in the assessment system. I don't--I think it's a blunt instrument, highly computerized, and prone to gross errors. At least I got a satisfactory result.