Is it worth buying specialist cycling shoes?

spds are fine for the road and cheap although if you think yopu will be mtbing in mud don't buy them save up for something else, they are shit in mud.

Wool insoles do, although they are quite thick, so reduce the fit of the shoe somewhat.

I tend to run most of my cycling shoes with insoles for this reason, except my DIY walking boot spd compatible boot, I forgot this rule and now have a pair of boots that work really well on rough ground but I can't fit my usual insole + thick socks winter set up, which is stupid considering that was what they were designed for. I'll make a new pair next year.