ive only bought one thing that in hindsight was a waste of money!
that is the 20ft fibre glass pole i bought when i first got my gear.i stripped the thing of the angle adaptor/pole hose and smashed it up(great therapy!!)and slung it in the bin the other week!!

my 22ft clx is now a conny roof/fascia pole
25ft hydra is spare back up pole
25ft SLX is my main pole.
i have an assortment of brushes but they are not wasted as i use most of em.
in hindsight i should of bought a 25ft SLX from the start but im quite sure the hydra and clx will come in handy to minimize downtime in an emergency.
i do have a small pole/brodex brush for washing the van which is a converted unger extension pole and it gets used every week.
i have a 30ft unger extension pole as well that i used before wfp but i dont ever use the 2 big sections.its mainly used as a 3 section extension pole for scraping birdmuck/paint off at height although i have used it as a traditional extension pole in severe cold weather.
regards
dazmond