when i did a trip around the uk coast (2 weeks and 3000 miles) we stopped in hostels,first time i ever did this and tbh it was pretty good,it cost us around £200 for the 14 nites and is much cheaper than bnb's and much nicer than camping you allready say you have the top box frame,right this all depends on how serious and how much ya gonna get to use it, but you can get a full frame top box and panniers for around £500 to fit yours,yes bloody expensive,but when you take into account you could get £100 for your topbox and frame,another £50 for the spare topbox your looking at £350 then take into account buying soft panniers (which you will sell if the touring bug gets ya) at a cost of anything from £50-£90 then getting the full touring works doesnt sound half as bad.and you can always sell the kit on if you dont need it anymore,and hard luggage as your finding out comes at a premium so depending on wear n tear i reckon you could get ya money back after 2 years use its a plan