As I see it, there are several benefits to having a survival shop with all the items a player could need.
1. Players can still sell items! If we set the buy price of every item in the server shop to three times the sell price, there will be a large window for players to sell items at that will encourage other players to buy at the player shops instead.
2. If we had lots of players who were very active, maybe it would be possible to get all the blocks you needed just by trading. However, at the moment we only have ten or so active players.
3. Some players aren't able to grind for hours to get things like dirt, sand, snow, and purpur. Some players don't go into the nether and/or the end due to personal preference. However, there are many players who don't get the same level of satisfaction from building in creative as from building in survival, even if they didn't get the blocks from conventional methods. If you build a farm to get the money to buy blocks, you still earned those blocks.
4. Most importantly, it's all about personal playing style. If you want to get all the blocks by mining or crafting them, go ahead. If you want to buy them from a shop, that's cool too. And if you want to get them by trading with other players, that's great as well. I think we should be less worried about how easy it is to get materials for building, and more worried about whether or not people can use the shop to easily grief other players.
Another option, or perhaps one we can utilize alongside the survival shop, is to have a mining world that resets every two weeks. There are several benefits to this:
1. It gives players a place to mine dirt and sand and such without feeling guilty about ruining the environment.
2. There's only so many blocks in the survival world, so when the server has more activity, we'll eventually run out of the non-renewable resources.
3. It adds another potential playing style to the game, one which many players are already familiar with.