I think however many toys you want and can afford, is the right amount to have.
You're not alone, I love having a really wide selection of sex toys. I have tried and loved clitoral vibrators, g-spot vibrators, anal vibrators, thrusting vibrators, butt plugs, ben wa balls, realistic dildos, glass dildos, anal balloon pumps, bondage gear, pussy pumps.... the list goes on and on! Why limit myself to just one?
I am trying to limit myself to only one or two toys in each category right now, though. It's pretty difficult, especially when a tempting DotD comes along... but storage is becoming an issue, lol. And if I have too many toys in one category - lots of similar vibrators, for example - it just starts to feel like a waste of money because I settle on my favourites and then I end up not using the rest of them.
I have just in the last hour decided to splurge on a pretty big item. I have about five different toys I'm returning because I don't like or don't use them, and finally decided that the refunds from that combined with Christmas bonus money means I can justify something I've had my eye on for a while:
If this leads to a sex toy machine obsession, then God help me. :P
What is it that holds your wife back from having sex toys? Does she just not like using them, or is she unsure what she would like? If she's scared of buying things in case she ends up hating them, let her know about Lovehoney's return policy - if she doesn't like it, she can just send it back, no questions asked. It might help her feel secure in being a little bit more adventurous. If she isn't very experienced with toys, maybe start small - a vibrating cock ring if you don't already have one, some nice orgasm gels or heated lubes, or a bullet vibrator. If she really doesn't want to try toys, don't force the issue - she might just not like them, and that's fine. Some folks just don't like sex toys.