I think elevation changes can give a circuit a lot of character. Obviously, this isn’t always the case, as Silverstone is very flat, but some of the best circuits have undulation. You only have to look at Spa, Suzuka, Austin, Interlagos to see this.
One of the main problems with street circuits is that it can hinder the chance for exciting on-track action, because it doesn’t yield many chances to overtake, which can be frustrating for many fans. But this is something you have to deal with when designing a street circuit. Is it going to be just using the actual streets of the city, or will it be a purpose-built track in the style of a street circuit, or perhaps a mix of the two?
Finally, as has been mentioned on here recently, having a great track is one thing, but what can make or break a circuit is the time of year that it appears on the calendar. Having it at the start of the year might be good, as it means the results are usually less predictable, compared to having it later in the year, when people have more of an idea about who will finish where. However, on the other hand, having a race at the back end of the Championship might be exciting for a different reason, as it could prove a vital twist in how the Championship goes. Lots to think about :P