(a) I agree that statement was an over generalisation, and you have clarified the point. There are also high power amps which sound good at low volume and don't have variable wattage. The Engls I've tried were that way though the tone wasn't really my style.
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(b) Assuming the budget of the OP is around £1k+ (a new Mini Rectifier is £1099) OP has a lot of choice, especially if they are willing to buy used (not everyone is). For example you can pick up a used Dual Rectifier on Ebay with that budget, though again whether or not it is a better buy than a mini is up to the OP. Here is a video comparison of both
http://www.youtube.com/watch?v=DXY53F03-lk
However looking at the OP's options I'd guess they aren't 100% sure of what they want just yet, as there is a massive difference in both tone and price between any Mesa Rectifier and an Orange Tiny Terror.
My advice would be to take your guitar, cab and any effects you use to a good shop, tell the salesman you are serious about trying some amps with a view to buying (I'd even ring ahead and let them know) and get them to let you try all the amps side by side with your own gear. PMT in Manchester were particularly helpful with me when I bought my Blackstar, the salesman helped in swapping cables so I could A/B things.
Thanks,
- guitarfishbay