Would like to have a meta command for add/remove that would work on a numeric value.

Right now you can set a value with

/lp user/group <user|group> meta set

What I propose is adding commands for add and remove:

/lp user/group <user|group> meta add
/lp user/group <user|group> meta remove

that would increase/decrease the meta's value by the amount.

The typical use case is where you give a player some meta value that represents a capability, and you want to allow them to purchase addition amounts that would increase this number.

For example, lets say I have a warp plugin that allows players to have a number of warps defined by a meta value. I could give them a default value in this meta, then allow them to use a command to increase this value that is run when the user purchases additional warps through a shop plugin.

Or perhaps the meta is the maximum listings in an auction house. With a shop plugin, the user purchases additional slots that are added by the command and increases the meta value.

Technically meta values are just strings, so in my opinion it doesn't make sense to implement a command to increment/decrement them.

I think this would be best served by the plugin which is using/modifying the meta value.