I've never been successful with the dream feed, but I was cluster feeding like you did at 4, 6, and 8, and I too found it very exhausting. I thought I would go insane nursing her all evening long. The way I got relief was my husband gave her a bottle for the 6 PM feed. At first, I pumped while he fed her so she'd have milk for the next day. After a month of this, I quit pumping and we gave her formula for that feed because I could never pump enough for a full meal (so she had some formula anyway), and because pumping was not really giving me a break.
Also, I just sort of got used to the cluster feeds. I just changed my attitude about them. I realized that sitting and nursing (while reading, talking to my husband or a friend, or watching TV) was actually more relaxing and a lot easier than chasing a 1 year old around....and all too soon I would be doing that. My daughter is 5.5 months old now, and our routine has changed, and nights have gotten very rocky. I miss the quiet evenings of cluster feeding and then sleeping for 6 or 7 hours.