I was on a stream last week that was basically like walking on softball or basketball sized marbles and my spikes/cleats came out very easily.  

I know that felt is generally a no-no for carrying invasive species from stream to stream but I considered getting a cheaper pair of wading boots with felt and would only use them for this specific stream. 

Worth it?  Would it make that much of a difference? 

It's a great stream but wading it is straight rugged and dangerous.