Something has to be changed with Incense
I have just had 3 incense popped in succession, and I didn't get anything other than Rattata, Pidgey, and 2 Gastly.
Would it be too difficult for Niantic to tweak something in their servers so that everybody could get a semi-rare spawn at some stage of the 30 minutes?
Answers
It's a spawn per 6 minutes if you are stationary, every minute if you are walking (from memory you need to travel at least 200m per minute to get the maximum).
Incense spawns briefly show the purple haze, but it doesn't show for long.
Your best bet is a walk along a river or other good biome.
Reputedly if you use it in an area with no Pokestops but good phone (cell) coverage you'll get random spawns rather than your more typical spawns (I've not tried it).
Incense spawns will have a purple ring around the pokemon, as opposed to the white rings you would see from a normal spawn.
Also, I popped an incense this morning and it spawned an 1171 dragonite. Yesterday, I had one spawn a seel, shelder, and a 880 poliwrath. Also spawned a good deal of starters during the event.
I don't normally use incense when I'm just sitting at home, but I went a little overboard and accicently bought too much.
In order to have a spawn per minute you have to move at 12km/h (7,5mph), so you can't walk. You have to run or to ride a bicicle or a skateboard, and it's not easy/safe to bike while catching.
You can't use it as a passenger in a car anymore because over 30km/h you won't be able to catch anything so, if it's the same for incese, you should travel between 12-30 km/h in order to be able to catch pokemon and have a spawn every minute.
So, in my opinion, incense are useless. Just use those you have until jenuary 9th so, due to the event, you'll get 1 or 2 starters.
I've used incense on hikes, walks along waterways, at crowded venues (like local fairs), at hotels, etc. and have never encountered anything besides the normal slew of the usual. So they're worthless IMO. I actually deleted some to free up space in my bag. That's one thing I would never spend money on.
Whatever spawns from the incense is extremely influenced (I can't stress this enough) by not only the biome you're in, but also specifically what spot you are standing when it triggers - i.e. the closest spawn point to you.
I've noticed this b/c I often go from downtown to the waterfront and watch the spawns change dramatically. By the waterfront it's all Magikarp/Psyduck/etc. with the occasional Dratini and rarely guys like Vaporeon/Slowbro/etc.
But even more specifically, I've noticed that it seems to pull from the available spawns from whatever your closest spawn point is. First I noticed that whenever incense spawned something when I was near a Pokemon on the map, it was often that Pokemon.
Then, as I learned the rare spawns better in my area for specific spawn points I would notice that sometimes my incense would spawn that rare Pokemon even when it wasn't on the map, or a different Pokemon was.
So right next to my apt. there is an Omanyte spawn point that has a chance to spit out an Omanyte every hour at :44. I've had my incense spawn one when walking by that very spot.
Granted, it seems there is still a small chance to get anything, but at the minimum where you're standing heavily influences what the probabilities of spawning are.
