Is it really a better idea to get cheaper speakers to get a better amp ?
No, I would spend $2 (minimum) for a pair of speakers for every $1 on amp assuming $400 is the starting point. That is just my opinion.
I'm almost about to buy the CF-70 speakers system on ebay.... can't find them in shops here...
I tried to find out where you are located because when I checked the Future Shop stock for the RC-70 I found one available in a Markham store for $1299. That is the lowest advertized price I have seen in Canada for that speaker. If there is in fact one left there I am quite sure you can offer them $999 or less if it is a floor demo. Many Paradigm supporters may not agree but I can tell you the RC-70 is in the same class as the more popular Studio 100. At one time, it was listed for $2,499 that is equal or higher (timing dependent) than that listed for the Studio 100 of the same vintage. It also sounds very close to that of the Energy flag ship Veritas speakers. Energy is now owned by Klipsch and they may not be too keen to continue R&D along the original Energy path. I think the RC-70 could be last of the original reference blood line so if you like their speakers this is probably your chance to acquire a pair of their near flag ship speakers for cheap (relatively speaking).
The RC-70 may not sound the best with a cheap AVR but for two channel listening, it should sound reasonably well. For 5.1, it should be quite decent when aided by a sub. Again, if you can pick a pair up for under 1K it is money well spent and probably future proof if you are not a never satified and crazy audiophile like some of us here are.