Adding manual vs. auto has been on our to do list for a long time. We will definitely add that. As for 1 and 2, there are dozens of attributes like those that we could add but we feel like it's important to keep the site as simple as possible. More of our thinking on this is in the FAQ here: Why don't you track more vehicle details?
it seems this question comes up ALOT in the forum... it seems to me there is more demand that you may think for this data. I know I have chimed in before
I understand wanting to keep it simple and not wanting to alienate others, but you are somewhat alienating those that WANT these features. Honestly I would most likley visit the site more, as I don't use the compare function at all, as the data is irrelevant and no comparative.
Perhaps you could add an "advanced specs" tab that is initially unexpanded. This would allow users who just want to input barebones info to do so, but for the many many people that want more detailed info, they could simply expand the option and choose away. The same goes for the research section. Start with all the models lumped together, then let us refine if we desire.
... but you are somewhat alienating those that WANT these features.
We know, and we're ok with that. I know that's hard to hear if you're in that group, but we feel like there are other sites that cater to car enthusiasts. And if there isn't a particular blend of features that you like at this site compared with other sites it's an opportunity to go out and make the thing you want to see.
If we had an "advanced specs" tab like you suggested, the disagreement would move to which specs we make mandatory. Someone would be unhappy that only two or three people choose to list turbo, and then the sorting argument doesn't come into play. If people don't use the features available, they're clutter. So we make the choice beforehand by choosing what to include. And we feel like we've hit on a good level of detail for the average driver.
I think tags or fuel-up notes are a good place to track octane rating. You can use those features to group similar fuel-ups together.
The current monthly bar chart is sort of a good way to look at trends throughout the year. We could probably add one more column to that chart so you could see the average for the current month. We're also working on a more interactive line chart that will let you specify time periods to look at.