I think that would definitely be worth the cost if you have a 7 in good condition. The difference in brightness of the 711 is significant, and $70 is not much for the upgrade. In fact, I am very surprised that it is no more than this.
Indeed, it is surprisingly reasonable. And MAC has an enlightened business model, as opposed to the auto-repair-shop model - I sent in my "newer" 7 for CLA and conversion as it had some other minor issues when I purchased it. The $70 fee is for when finder conversion is the only job, when it's done as part of a CLA the adder is only $50 since there's a duplication of some of the work between the two jobs.