I've been grinding through the many punishing levels of this trilogy and have found a few tricks some may find useful.
The first is the levels in Crash Bandicoot 1.
Two especially grueling levels : Road to Nowhere and High Road. Here I found you can run along the two ropes either side of the bridge almost the whole way to the end. The clip is short but I've used it a lot try to get the gems. Be wary or your footing it is just like a tightrope.
Here's a link to the video:
Second is in the Crash Bandicoot 3: Cortex Strikes Back game , versus the 2nd boss Dingodile.
If you spin directly after a sliding jump (I believe) you gain a small amount more height and hang-time.
Here's the related video:
Try these out, let me know what you think in the comments section. Does spinning let you slide-jump higher? Did I just set a World Record for beating Dingodile? Game on.