I'm on the other side of the fence honestly, in that small reward for my character so don't want to spend a lot of time there. Objectively though, I'll toss my feedback in too, after reading everything.
I've played Mari, Jenna, Ruairi, and Tarlach. I've played live for a long time, giant as main but plenty of time on other chars mainly to familiarize myself with other skillsets. I feel the balance of what's available from the shop, both in terms of skillsets and design, are pretty good. Unfortunately, I've only made it to probably 26-28F range, since I've only soloed. All in all, take what I say with a grain of salt since end game tends to be the primary focus.
The risk/reward... Normally you'd want to more carefully consider before messing with it, 10% more XP+Gold doesn't sound like much most of the time, but this alone can make a huge difference in incentive, grind time, and even comfort zone. There seems to be some rather nice rewards from SP, so I'll say that boosting incentive is a double-edged blade in drawing more people wanting to run it but also because more of the rewards will be circulating in the player market and thus lowering the incentive for newer players to investigate SP. After all, if the point is the rewards, and there's ample of it, most will get what they want off guildies and a good chunk of the remainders will likely just throw up a buying ad.
Anyone still reading, will likely also know that more than just practicality, the overall mentality of a community, in anything and not just games, can be the end all be all. Aesthetics are a pretty big deal, despite similar stats players will still avoid something that is clearly designed to be ugly over something that was meant to be appealing, but reserved. In fact, people aren't shy about sacrificing extra stats for fashion until in very high pressure content.
From here, I'm just rambling about things to think of for redoing some rewards.
I don't think a slight boost to xp and gold would be a major problem. I personally would like to see more "Junk" type rewards, rebalanced. I'm not saying place highly desirable items. However, shift firewood to average or fine, quantity of 3-5 maybe. Fine Handcrafted Bandages, Wound Remedy 30 or 50 at higher rewards, 30 pots if they're mixed, 50 for more normal pots, etc.
Point is to make stuff that people aren't normally gonna go out of their way to farm or probably even buy, but there could still be value in holding on to it. 10 Firewood, yeah there's a bit of value, but as a general mentality it isn't perceived as interesting as 2-3 average firewood, better is that the rate and size makes the average more worthwhile to keep on a pet. As a bonus, they're not going to have to go out of their way, like SP all the way to Dugald, to refine some rather awkward and high quantity items to make them worth keeping regularly. While going as low as 1 may be fine, I honestly feel like it's going to feel more as an insult than a reward.
Unless the buy value off an NPC for the items you're getting exceeds 2k, I would strongly advise against putting in rewards that can be bought from generic stores. Fabrics can be bought, but get expensive quick above Cheap. Bandages can be bought, but are really cheap and don't NPC for much of anything. Fine Handmade Bandages are rather effective, but won't frequently be used still cuz it's easier to just nao or use the healer most the time. When Nao's not available many people lose drive and just want to afk anyway. Leaving the usefulness to the general population, as honestly rather low. The biggest concern is likely going to be fragmentation of some rewards like this.
Things I think are rather shy to be used as rewards but I honestly feel would have more value even at "lowish" quantities, would be herbs, holy water, or stackable PTJ materials even. Note the stackable, I doubt people will be pleased to get 10x apples as a reward suddenly, but 10 wool or something is more of a "don't want it but I know someone else who runs this might." The rate to acquire and number used for a PTJ are pretty different, but the space used for each can leave a rather bad impression for the apples.
And I'll end with saying, you're doing an RP dungeon, no matter the difficulty bear this in mind. It means you don't lose consumables, and dura only ticks from idling. This is likely why crystal costs are so high, but also means you're not running off to restock and repair to continue. For this reason, I can not advise high level pots and/or high quantity of restoratives in return. Doing SP is pretty wortwhile if your Naos are low as is, having it basically be the "My naos are down and I need to restock, SP while I recharge 2 Naos will have me good for a few days" raises a red flag in my mind, though others may disagree.
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