Hi -Q to OP but if you've already done Nouveau's Express lash training, why do you want to go on Lets GO? Lets Go IS Nouveau's Express lash training - it's just under a different brand name (used to be Blink and Go). So if you've already done the express lash training with them, I'd phone them up and see whether you need to do Lets Go. I guess the only thing you'd want to consider is whether you want to be listed on their Salon Finder under Lets Go - but that would only be relevant if you had a lot of clients looking for the Lets Go brand. This is quite a new brand for Nouveau, so I'm not sure how many clients its likely to pull in, but they do seem to be doing quite a bit of marketing for it, so you never know.
Having done the course myself, I'd say I think it IS worth it only to be able to offer clients a variety of different eyelash extension options to choose from, but it hasn't been as popular for me as I'd first thought. Having said that, I haven't gone back for my 'graduation' day yet, so am not yet listed on the Salon Finder.