Tempo Sync'd Effects and Tempo Changes?

This is very common. The best way I've found to deal with it is to hard set the delay instead of sync. If you want the delays to follow the tempo, setup the delays on separate busses and hard set the tempo on each delay for the tempos you want to use, then use two sends to switch between them.
 
Regards,
Dan
 

brundlefly
Reducing the number of changes may help. If you draw tempo changes in the tempo view with snap disabled, you can generate dozens of tempo changes per beat. Musically, there's no need to have tempo changes between note events. So if the shortest interval between notes in the region is 1/16, you should set snap at 1/16th.

This is key to proper performance when having gradual tempo changes. Often you can live with one tempo change (at the 1st beat of the bar) or with 4 per bar (every quarter note). That usually works well with all software synths and delay effects. Interestingly, external gear (at least what I use) seems to work a lot better in that respect, but hardware synths and FX can easily cost 10-20 more that a native software version, so you would also expect them to work better.
 
For hard tempo changes (e.g. different song sections at different tempo) you could also use 2 delays that are hardwired to a tempo (but you need to calculate and specify delay time in ms not in musical measures otherwise it will again follow tempo changes and cause artefacts) ... Sonar aux tracks would be an option. feed the aux track from the same guitar track, route them to the same bus, stick different tempo delay in each and use automation to fade in and out. in this way you can do cross fades if necessary which often sound a lot better than hard preset changes.
 
 

One technique you can employ is to automate the tempo-sync setting, turning sync off during tempo transitions. This may not be necessary for every tempo change, but for places where you can hear an obvious glitch you can temporarily let the delay run freely for however many beats it takes to complete the transition. There is usually no downside to letting the delay fall out of sync briefly. In fact, it'll sound far more natural whenever the tempo change is drastic.