I have clients who were extremely impressed by the improvement in video operations of existing color analog cameras upgraded from 320x240 DVR recording (and viewing) at low frame rates to full resolution server-based recording and viewing at high frame rates, using encoders.
I'm most familiar with the Axis encoders, although I know there are some other brands of good encoders out there, and most integrators with whom I've discussed it have their own preferred brands. The encoders I'm familiar with provide multiple video streams per camera, each at appropriate settings such as for live monitoring, recording, and remote viewing.
Encoders can add all kinds of capabilities to each analog camera, including video motion detection, video loss alarm, alarm events including sending video clips or frames via FTP or email, activation of the encoders physical alarm outputs, and PTZ support including activation of PTZ presets upon motion alarm. This is without any server or application software supporte needed.
Some 4-camera encoders provide a 1536x1152 quad view. One series of encoders supports up to 64 GB memory card per 4 cameras for edge storage. Edge storage combined with the free 16-camera software make a heck of an afforable upgrade for a small analog camera system, as for some end users this means no NVR or DVR needed, and any recent model PC or laptop could be used given edge storage.
On the other hand, for one client I'm upgrading two facilities with network cameras, and moving a DVR they recently purchased and a dozen analog cameras from one facility to another. There is no network in the facility's remote building, and the analog cameras and DVR will work just fine there.
I'm a fan of reusing good analog cameras, and find that encoders can provide excellent integration into whatever VMS is being used. But also find that I can reuse existing late model DVRs, especially in circumstances where there is no live monitoring.
The product life cycles for most good analog cameras is pretty long, and they are often good at covering small indoor areas very well.
I don't find much use for new low-end or "entery-level" DVRs though.