Hello, ladies and gentlemen.
As I'm a huge fan of numbers, Excel, and MOBAs, I'll try to theorycraft a little on my spare time.
As I don't want to start with something extremely complex, this post will deal with boots. Are they worth their gold cost ? Basically, it is a simple comparison between their total purchase cost and the value of their stats. For example, the cheapest SP item, the Apprentice Wand, costs 450 gold and gives you 20 SP. You can reasonnably think than 1 SP = 22.5 gold.
Long story short, here are my findings:
Stats (in gold)
Warrior Boots are worth their price. They are not truly awesome, but this is a very safe and effective bet if you mainly deal Physical Damage. Moreover, they are cheap, so you can get them fairly quickly.
Conclusions and analysis (STATS do NOT include the active property of an item):
Riftwalker's Shoes are a bit tricky, because they cost a lot and give you an active property (a teleport). As a teleport scroll costs 120 gold, you have to use these shoes at least 6 times for them to be worth the price. However, the great casting time of teleport (8 seconds) makes them kinda unsuitable to gank (a lot of stuff can happen in 8 seconds, like your friends dying and/or your foes retreating). This pair of boots is a high risk bet. The other boots are awesome and cost less.
Monk's Shoes arevery good. Although they are kinda expensive, the 10% CDR is okay, but the Resilience is what makes them absolutely awesome. 35% resilience means that Crowd Control cast on you is 35% less long (so instead of being stunned 3 seconds, you'll stay stun only 2 seconds). Of course, if the enemy doesn't have any CC, they are expensive and useless. But against a CC-heavy team, these boots are priceless. Items giving Resilience are very rare (and they are worth building on attack damage heroes only: check Relentless Cape and Hiro's Windblade).
Charger's Sabatons are (almost) exactly worth their price if you forget the active property. The active gives you +25% Movement Speed when engaging (when you are going closer to an enemy). These boots are not a troll item even on heroes not needing the active (as they are worth their price even without), but they'll probably be a must have on initiators (like bruisers) or assassins needing to chase a fleeing target.
Acolyte Slippers are defintely worth their price. No special active property, just raw power. Boom. Probably the best choice for mages, unless the composition of the enemy team makes you choose Monk's Shoes (for CDR, always useful on a mage, and Resilience, useful against those damn OP-stunning-unkillable-waytoopowerfulOMG-heroes).
Messenger's Sandals are tricky. Basically, the extra MS too expensive to be worth the cost (and as the other boots are great...). However, a small advantage in move speed can give you the map presence and the range necessary to kill that damn enemy hero while this chicken tries to "run" away. These boots are a good choice for junglers who want to gank a lot and need the extra mobility to catch people (melee junglers ganking only occasionnaly can prefer Charger's Sabatons for the extra armor and the bigger (but ephemeral) boost).
In conclusion: boots are generally awesome. They are definitely worth their price if you pick the right (and the left) ones. Moreover, the extra mobility will make your poking easier to land, and will save your life/give you the ability to take someone else's a lot of times. I recommend buying Commoner's Boots quickly (at your first trip back to the base, or at the second, but hurry up), and buying better boots as soon as possible (as soon as you don't have something extremely important to buy).
Thanks for reading my article. I feel like what I said is a bit obvious and useless, but I wanted to start with something simple that concerns everyone (because everybody buy boots, right ?). Feel free to tell me what you think about my post. And sorry for my unstable english, it is not my native language.