I really don't get this kind of post...
I understand that you are frustrated that things are not as smoothly running as they have in the past, but from your own description of your site, why are you still on a shared server?
It seems as though you have enjoyed a "gravy deal" for most of that time; you got what effectively performed what you needed it to for very little money. If times have changed, and the host changes, why is it so hard for you to realize it might be time for you to change also?
The hugh growth in users fueled by the aggressive marketing and pricing has led to some infrastructure problems being exposed, and the pitfalls of running business sites on shared severs being adequately demonstrated. Hey, it's great that it worked for you in the past. It has worked well for me in the past also.
None of those changes have anything to do with a host being "professional" - everyone has a different definition of that depending upon their reference point, experience, and attitudes. They do, however, bring into serious question the wisdom, or advisability, of hosting e-commerce site on shared servers where you do not control all the other users on the server.
The advisability of relying completely upon shared hosting style shared email servers for business/ecommerce use is even more questionable.
I don't see what the problem is. Evaluate the service you are receiving, make a decision (or decisions) as to whether or not Dreamhost remains a desireable cost/benefit value, and either stick it out, or move to something more appropriate for your needs, depending on how this all works out in your mind. Simple.
Well, it ought to be easy, should take very little time, and "hitches" should be managable and minimal. The difficulty of moving a site between hosts is something that is of your own making, because of decisions you have made regarding tools, technologies, etc. I'll grant you, if you relied on the wealth of services a typical Dreamhost account provides, and utilized them fully, finding an appropriate host to "move" to, at a cost your client will not balk at, could be challenging.
The end result of the recent issues have forced responsible web administrators to make these evaluations, and the "right" answer is not the same for everyone. None of my e-commerce site clients are thrilled with the last month's performance. I've found some alternate hosting arrangements (at greater cost) and have presented those alternatives to my clients, which is a respopnsible thing to do. My client's are business persons, not techies, and they make their decisions on this kind of stuff based on their business plans, profit and loss posture, and business experiences...not emotions.
None of them has yet decided it is worth more money to change from Dreamhost, and are waiting to see if things stabilize.