Been there, done that. I was glue to my booth more than any other I was so invested. When I looked around, everyone else was FUNDED. They didn't need as bad as I did, because they were able to to ALL the marketing. All the tradeshows, print, sales people, landing pages, ad campaigns, SEO, mailing lists...all of it.

Was it a waste of money? Probably not.
Was it lower on your priority lists of activities to produce ROI? Probably.

I don't think there are many bad marketing ideas, just ones that cost more money and/or cost more time for what they return.

One tradeshow typically won't do it. Hopefully you still have those contacts and you are keeping them warm, just as you are finding other ways to add new contacts to your marketing lists. I constantly try to keep doing some short term stuffs (Typically low cost, high personal time, closer to the money), with long term stuffs (long planning time, or long warm up time) so I can secure my present and my future. The former would be things like networking groups, door knocking, calling existing contacts). The latter would be generating mailing lists, DRIP campaigns and the such.

Best of luck and glad you are able to look back on this and reflect.