This line alone shows you don't fundamentally understand the currency. The Cryptographic hash of the transaction block exhibiting specific, tunable properties (matching a number less than 'x'): was not chosen at whim. You should read the first reference in Shatoshi's Paper:
W. Dai, "b-money," (1998)

It explains that you can't do useful work while protecting the integrity of the system. The requirement to do "useful work" would allow dishonest participants to "cheat" by not actually doing the "useful" part of the computation.