When assigning a variable with several parts, the $+ is allowed. To call (get the value of) a variable with different parts however, you need either $eval() or []'s. Here is a working example:
alias server {
/set %servername $+ %numero $1-
/echo -s [color:Red]%[/color]servername [color:red][[/color] $+ [color:red][[/color] %numero [color:red]][/color] [color:red]][/color]
/inc %numero
.server -m %servername [color:red][[/color] $+ [color:red][[/color] %numero [color:red]][/color] [color:red]][/color]
}
