It's not a crazy idea at all EasterRobin although I completely understand the people who say it's not worth it and you make pennies. You have to be dedicated.
I have just cashed out another £2.50 in Nectar points in the last few minutes though! I have made so far this year £135 in nectar points which go a long way towards groceries but better you max them in the Tu sale, or for meals out or save them for Christmas if you can.
Head to a website called the MoneyShed, and read some of the forum posts on the subject for some tips, because when you've been doing these surveys a while you start to notice patterns and learn little tricks.
I would say, always, always cash out as soon as you can, these sites could close down at any moment and you don't want to lose your hard work, always be honest with answers (they do audit from time to time) and if they find discrepancies you will have your account blocked.
With Panelbase you often get invites to join other platforms, so for example I sometimes now get invites from GFK, they send me surveys that take 2 minutes to fill in then I get a link to cash in an E voucher for £1 (not a lot but for a minute or 2 work) I choose Tesco, I have a folder on my computer to store vouchers (have £12 Tesco so far) and save these for Christmas. Panelbase also pay well for product tests - I got £20 for testing a mid range face cream, they are always mid to higher end products like Olay or Garnier and you get to keep the product. I have had loads of tests from them, anything from chocolate to shampoo.