Diablo III: Reaper of Souls

Would the game be more enjoyable now than it was, if I decided to start again from scratch? or is most of the new changes focused on the higher levelled people?

Also a rather silly question to ask, but the loot changes and stuff was released as a patch right? I don't need to buy the expansion?

The leveling experience is much more rewarding than before since general items have more useful stats, especially with Smart Loot making 50% of your items have stats you can use, Act Bosses drop a guaranteed legendary for your first kill when you're below the level cap (60 now, 70 in RoS), and monsters scale with your level.

Not that much sense in stocking up on materials right now, as for level 70 equips you will need a different set of materials obtained only from salvaging lvl 61-70 equipment which are not currently available.

What I've been doing now is working out what build works best for my different characters and leveling up those paragon levels.

Stocking up materials for Reaper of Souls only facilitates the leveling from 1~60, where those materials may be used. There are a few items that would be very good to be crafted, but most don't require excessive amounts. What I've found with crafting so far is that I can farm the pomegranate out of Common Debris quite easily. Most recipes don't require many Exquisite Essences, but the ones that do require a ton. Gehenna's are 48 and Wondrous Deflections need fucking 80 and I've burned through my stockpile of 1000s. Some of the lower level sets have slots that require a lot as well. Iridescent Tears don't salvage as much per drop, but rares are a lot more common than magical. If you're playing on a lower difficulty (Normal~Expert) you'll probably be finding enough loot to craft a fair amount, but higher difficulty, you'll be outleveling your crafting range quite quickly.
I would recommend buying the Cain's set recipe, and Captain Crimson's. Cain's gives a decent EXP boost, and Captain Crimson's Bowsprit (Pants) rolls IAS and Block Chance at 30.
If you play some Reaper before-hand, instead of starting the Crusader or any other character at launch, you could find a level 70 weapon with up to -22 Level Requirement, if I remember correctly.

A few WoW buddies and myself did a grind session on the Mira quest for a few hours. Quite a few legendaries for the each of us and nearly 25 Paragons per each of us.

Mind if I join you sometime?