There's no simple answer to your question.
First of all, if you've really enjoyed your experience with LE8 and would like to stay as close to that as possible, you may just want to buy a Logic Express 9 upgrade. So far, LE9 seems to run just fine on my iMac with Mavericks. You can still find upgrades if you look hard enough, like at Amazon, for example. LE9 was a really nice upgrade from LE8 while retaining the same basic look and functions, so you will not experience any culture shock.
As I alluded to previously, the new GarageBand is almost more of a Logic Express X than an update of GB. But it looks and functions very much like Logic Pro X, which is very dramatically different than any previous Logic, Pro or Express. You WILL experience culture shock. However, GB 10 is not a toy, but a very powerful program. And it's FREE! If nothing else, you get the Drummer Track with GB 10 which is fantastic.
It really depends on which features you particularly like in LE8. If you can live with the black lines, stick with LE8. Or upgrade to LE9, which should eliminate the lines. And maybe give GB10 a try. You can always just uninstall it if you don't like it. And if you fall in love with it, you just might end up buying LPX.
