I don't see the point of t-shirts for any distance. I do train in some of them but you end up with piles of the things. I think they should be an option you can buy if you want them (thus marking the event should you so wish). I loved Bramley 20/10 this year where we got towels, now that is useful. Apparently they go hats last year, another useful momento. I've just put a load of old race t-shirts in the recycling, most of them have never been worn. A shame and a waste.
All races are significant though.