I can't comment on the lens, but I will say this when it comes to money:
in·vest
- verb
1. to put (money) to use, by purchase or expenditure, in something offering potential profitable returns, as interest, income, or appreciation in value.
2. to use, give, or devote (time, talent, etc.), as for a purpose or to achieve something.
We spend money on paying bills and things we need to survive. We also spend money on frivolous purchases that we could really do without. Do you need this lens? Are you limited creatively by what you already have in your arsenal? Will this lens add value to your collection?
If yes, then this is an investment.