I do collect both theme. Just like you, I'm attracted to the new Castle theme as well. But i didn't manage to collect all of them especially the big set as my priority is still Star Wars.
Buying Castle sets have more minifigs which fasten up the process of building army @ a reasonable price & there are metallic pieces too. I do duplicate some of the small sets like 3 each for 7009 Final Joust, 7090 Crossbow Attack, & 7040 Dwarves' Mine Defender & 2 sets for Knights' Catapult Defense & Skeletons' Prison Carriage, & Castle Battle Pack.
But still I limit myself on those Castle sets as my purpose of collecting LEGO is because of Star Wars. All you have to do is to purchase the theme that you really really like & if you think that you can't keep your collection for a long time I think you should buy Star Wars theme as they have market value. But for me, I will keep them.
Anyway both theme is a great theme, & fair since now both theme have parts made in China.
So Castle has a reasonable price, & more minifigs (the main reason why people are purchasing LEGO) & even have minifigs pack or you can purchase them from pick a brick.
Still you have to know which theme you really like.