I actually tweaked the harvestables in Sinking Sands myself. What I did was twofold: one, I made some of the areas (generally coinciding with patches of green) where harvests can spawn slightly larger, and slightly increased the number of harvest nodes that would appear in that area at once. And two, when there was an area set to spawn "gathering/trapping" type nodes (ie, den or root or bush), I changed the ratios from an equal chance of getting any of those nodes, to be slightly more in favour of roots. These changes apply to the beaches, and the areas above the cliffs, but I left the Twin Tears and the islands areas as they were for now.

That said it will still FEEL like more rares than before GU37 for three main reasons:
1. bushes now drop roots, so if you regularly harvest bushes, you'll end up with a lot more roots than you would have when they had no rare
2. nodes with 2 rares will drop rares more often. Previously they were dropping rares at the same rate as other nodes which had only one rare. This meant that they were actually dropping each individual rare type HALF as often as the rare from a single-type node like roots or dens, meaning only half as many rare loam, ore, soft metal, and gems were entering the world as rare roots or pelts. So yes, these will now drop at the same rate as rare pelts.
3. the level at which you start using the bonus result table is now lower. Prior to GU37, none of us could even use the bonus harvest result tables for T7 (OR T6) at all. Now, we start having a chance to.
For those who don't know what I'm referring to with the bonus result tables, harvesting works as follows. (If you really don't care about details you can skip this bit.)
For each node in each zone, when you harvest it, there are different result tables set up that tell the game what to give you when you harvest. Your skill level determines which table you use.
For example, using entirely invented numbers, let's imagine that there is a root node in a level 30-40 zone and you go and harvest it with a gathering skill of 190.
The game sees that the root node points to two result tables. Let's call them:
T4_roots_base_result - required skill 140
T4_roots_bonus_result - required skill 189
* The "base" table might tell you that you have a 70% chance of getting 1 root, a 20% chance of getting 3 roots, an 8% chance of getting 5 roots, a 1% chance of getting an imbue, a 0.7% chance of getting a rare root, and a 0.3% chance of getting a rare root + 10 common ones.
* The "bonus" table might tell you that you have a 60% chance of getting 1 root, a 25% chance of getting 3 roots, an 10% chance of getting 5 roots, a 0.5% chance of getting an imbue, a 0.8% chance of getting a rare root, and a 0.7% chance of getting a rare root + 10 common ones.
(Yes, the numbers probably don't add up to 100%, I just invented them on the spot.)
Now we know that if your skill is under 140, you can't harvest the node at all. And we know your skill is 190. So the RNG rolls a number between 140 and 190. If it gets 140-188, you use the "base" result table. If it gets 189+, you use the "bonus" result table. Clearly, as your gathering skill increases, your chance of using the "bonus" result table gets better. (This is where +harvesting skill items affect your results, they increase your chance of using the bonus table.)
As of GU37, you get to start using the "bonus" table at level _8 (so, 8, 18, 28, 38, etc.) You're still not guaranteed to use it, but you have a CHANCE to use it. Previous to GU37, the level at which you could start getting the bonus was much higher, so that you didn't even have a chance to get the bonus table until you had entirely outlevelled the tier. In T6 and T7 prior to GU37 we still couldn't even start using the bonus level at level 70 with 350 skill, so we've been harvesting off the "base" table all this time. Now we will begin to have a chance to use the "bonus" level, so yes, we'll get slightly better harvesting results in T6 and T7 than we were before, but it's actually about the same results as we would eventually have got as the level cap raised and we continued to level up.
Incidentally, all nodes within a level range (in this example, all nodes in level 30-40 zones) point to the same result tables, so it makes no difference whether you're harvesting in one zone or another.