As one who has tired of Mahler...
i can not ever imagine getting tired of mahler... inconceivable to me. but i guess it would be boring if we all felt the same way.
anyway, here are two more to add to the list:
alfredo casella - his 2nd and 3rd symphonies in particular. in the 2nd there is a wonderful mahlerian funeral march and in the third symphony the slow movement reminds of some of mahler's last works. brilliant music, at least to my ears.
another one i would mention is the second symphony by franco alfano.
as many other comments already pointed out, the earlier symphonies by wellesz have some fascinating qualities especially in the slow movements. i also would love to learn about more music in that vein. i guess the challenge is that the more the tonal envelope is being stretched, the stronger the temptation there is to sacrifice emotion for an imbalance in favor of the left brain.