Best decision I ever made was to add pressure washing to my bussiness.
Hard floors might be a better earner but the avaliability of work is smaller you will find your self travelling bigger distances.
walk down any semi-detached street and you will see drive after drive that needs cleaning and every home has paths or a patio round the back so the market is huge, I still work in the same 4mile radius that I aimed for with my carpet cleaning (I rarely leave my small town)
If I could pack in carpet cleaning altogether and just do PW I would, the job value & hourly rate achieved is much higher.
I started of for the first 2yrs with a techclean 13hp Honda and 18inch FSC an adjustable lance and a turbo lance, cost me £1300 5 years ago