Is all attachment equal in nature? In the general view of "attachment" in Buddhism, is the quality of attachment considered to be the same across all possible types of attachments? Or are there different qualities or degrees of attachment? 

Put another way, can one kind of attachment be considered "less bad" or "more bad" than another kind? Or is it all just "attachment" in a general sense, without distinction?

For example: Is clinging to the nostalgia of an old childhood friendship any different than clinging to money or cars?
According to my first teacher, attachments to concrete worldly things are not as bad as attachments to abstract principles - which generate massive conceit and world-scale aversion.

Compare attachment to tasty food with attachment to religion - which one creates more suffering?

In my understanding, the way attachment works is via appropriation of a dharma (an object of mind) which then creates the duality of "this" vs "that" (and its special cases, "I" vs. "you" and "us" vs. "them"). There are four major quadrants here:


Low contrast between "this" and "that" and small scale of identification.
Strong contrast between "this" and "that" and small scale of identification.
Low contrast between "this" and "that" and large scale of identification.
Strong contrast between "this" and "that" and large scale of identification.


An example of the first kind is attachment to certain flavor, like the taste of some food cooked in a particular way. Even if one can't find this specific cooking style, one can find fairly similar kinds - and the resulting aversion to other flavors will not be that strong. In this case suffering generated by this attachment is both weak and small-scale (only applies to one small area of experience).

An example of the second kind is attachment to one's own life. Here the contrast between living and dying is very high, but the scale of identification is rather small. So even if one's fight for survival manifested as external violence it would unlikely create a world-scale conflict - so the suffering will be strong but not vast.

The third type can be explained on the example of attachment to gender identity. In this case the scale of attachment is massive - one identifies oneself with "I like men" or "I like women", but the contrast between the two is not polarized enough -- not black and white enough -- to create a major issue, like a war between genders. There are certainly some very common tensions between genders (can we call this "very weak but vast suffering"?), but very few women would say that men are harmful and should not exist - and vice versa.

Finally the fourth type is attachment to an abstract and highly polarized view or principle that is very prone to emergence of group identity - such attachment to religion. In this case the contrast between "good" and "bad" is very high - the carriers of the other view are considered harmful and evil. And the scale of identification is very large - all carriers of the same view are considered "us" and all carriers of the other view are "them". This results in a very explosive combination of "good us" vs. "evil them" - hence strong and vast suffering.

And then of course there are all kinds of intermediate qualities between "strong" and "weak" and between "small" and "large".

In your example, the difference is in the real object of attachment. If the reason you attach to an old childhood friendship is because it exemplifies some abstract quality that your old friend possessed that you now idealize (and on this basis cultivate aversion to those lacking such quality) - than that could be a fairly dangerous attachment. On the other hand, if attachment to old childhood friend is solely on the basis of her beautiful voice - then it's not such a big deal.

Similarly, if attachment to wealth is on the basis of simple idea that wealth gives one access to comfort and material pleasures - then it may be a medium-contrast/medium-scale problem. But if attachment to wealth is part an abstract view that all wealthy people are smart and hard-working and poor people are lazy and immoral, - then it could be feeding a global-scale conflict.

To summarize, whenever you want to evaluate an attachment you should
 - identify the real object of attachment, the root of attachment (aka the preconception)
 - assess the degree of polarization between the object of attachment and its opposite
 - assess the scale of identification and the size of the potential conflict

As a rule of thumb, watch out for abstract and highly polarizing attachments - they tend to create the strongest and largest-scale suffering.