Lore Mastery (as described in the Warlock & Wizard Unearthed Arcana document) grants this ability at Wizard level 6:
At 6th level, you learn to augment spells in a variety of ways. When you cast a spell with a spell slot, you can expend one additional spell slot to augment its effects for this casting, [...]
An additional 2nd-level spell slot can increase the spell's range. If the spell's range is at least 30 feet, it becomes 1 mile.
Now, suppose I use a 1st level spell slot and a 2nd level spell slot to cast Unseen Servant. Although this increases the range from 60 feet to 1 mile, this is the only reference to range in the spell's description:
The servant springs into existence in an unoccupied space on the ground within range.
If I want to tell it to go a mile away, grab something, and come back, I'm out of luck:
If you command the servant to perform a task that would move it more than 60 feet away from you, the spell ends.
So increasing the range only changes where I can spawn the little guy, not where I can send him. However, I think this might still be abusable: Could I have the Unseen Servant appear a mile away and command it to pick an item up, then move 15 feet closer to me? I would repeat the movement every turn until it arrived.
I have thought of two potential problems with this.
How do I command something a mile away? Well, the spell description says that you "mentally command the servant", so I see no immediate issue with communicating with it over a long distance. There might be a limit elsewhere in the rules, though.
The wording about the 60 foot limit seems ambiguous to me. After it moves 15 feet towards me, it would still be more than 60 feet away from me, so you could argue that the spell would end immediately. However, the wording is "move [...] away from you", and it would only ever be moving towards me.
Would this work the way I hope it would?