In my case there is, but I'm a little hesitant to go into all the detail of that. I don't want to start a discussion about "who got what, and when, and for how many cookies" because my plan has "evolved" to be a bit of a "hybrid" as a result of multiple reconfigurations.
I expect that exactly what might be involved will vary from user to user depending upon when they signed up, what plan they initially signed up for, and what plan changes/addons they may have added over the years.
Things like VPN users, unique IP addresses, secure servers are likely to be involved, as these features have come (and gone - but mostly come) with various plans over the years and at various times. I'm not trying to be evasive, I just don't feel the "particulars" of my "hybrid" plan are relevant.
I'm only basing what I would "lose" if I changed plans on what my panel shows as my feature set, and yours is likely to vary somewhat from mine. My price also varies, because it is presently based on the old "Code Warrior" plan, minus a "reseller's discount" from a now-defunct reseller program that was in place years ago. This places it at more than the latest "Code Monster" price, but lower than the old "Code Warrior" price, but with slightly different features than either of those plans.
Now, if I add up all the "addons" (or what would become addons under the new plan), I will end up paying "very close" to what I currently pay to retain the same features - hence the difficulty in deciding whether or not I want to lose some of the features, and save an almost insignificant amount of money, or keep the features and continue to pay my current price.
I will say this though: I can't imagine you ending up losing value with DreamHost. They have been very careful in every instance I have dealt with them to "fudge", if at all, in my favor and reward me for the longevity of our business relationship. They value their customers, and have always demonstrated that to me.