What you mean by your picture quality are really blur before you install the signal amplifier?
Picture become pixellite or frequently stuttering?
Based on my very limited knowledge, Astro was transmitted using digital signal... and digital signal are only ON and OFF...
Your picture will be always same when adequate signal can be received by your dish and LNB... regardless signal quality are higher or not, same quality of picture will be shown on your TV screen.... Picture quality are determined by Astro itself, at their broadcast center.... their compression method and bitrate that they use to transmit the signal to measat satellite...
And if low signal are receive by your dish and LNB, as I said above, your picture will not blurry but it will become stuttering like when you watch stretched DVD or VCD, and when raining come to your area....
Sorry to say, maybe that's just a placebo effect.....

You can search all of old Byond thread, there are a lot of discussion regarding signal amplifier....
Up to u to believe it or not, i know what i am talking about becos its not through my knowledge, its through my actual usage that give me the actual benefit n not placebo effect.