Lightning network and sidechains are not magical things, they're orthorgonal and not alternatives to relay improvements. But since you bring them up: They're both at a _futher_ level of development than IBLT at the moment; though given the orthogonality it's irrelevant except to note how misdirected your argument is...
I appreciate the further detail that you describe regarding the relay situation. So it seems that you are not optimistic that block propagation efficiency can have a major benefit for all full-nodes in the near future.
Yet block propagation overhead is probably the single biggest argument for retaining the 1MB as long as possible. To cap volume growth to a certain extent.
I'm not sure about that. My opinion is that the biggest argument for retaining the cap (or, at least, not introducing a 20x plus exponential increase or something like that) is the burden on full nodes due to (cumulated) bandwidth, processing power and, last but not least, disk space required. Of course, for miners the situation may be different - but from my own point of view (running multiple full nodes for various things but not mining) the block relay issue is not so important. As gmaxwell pointed out, except for reducing latency when a block is found it does only "little" by, at best, halving the total bandwidth required. Compare this to the proposed 20x or 8x increase in the block size.
Bandwidth is always a much bigger concern than blockchain usage on disk. TB disks are very cheap, v0.11 has pruning.
Block (1) validation time as well as (2) propagation time are both issues for mining security and avoiding excessive forks/orphans which prolong effective confirmations.
They are separate issues however, and you can have either problem without the other in different blocks, or both together.
Both of these are exacerbated by block size.
As eager as I am for a block size increase for scalability, I'm not convinced that it is yet warranted given the risks... The developers are aware of the issues. They aren't goofing off. It is just better to get it right than to get it done.
Validation time, in its self is not an issue, miners have approximately 10 minus to validate, the issues is not the time, it's that you can hack the protocol and validate nothing or force your competitor to waste time validating to gain an advantage, (this is also a temporary hack and if anything highlights where development should occur)
Propagation time is a feature not an issue, (a symbiotic byproduct) that adds to the incentives that make bitcoin work.
their are hypothetical issues with how these features could be abused, the problem is the developers are not separating the hypothetical issues form the features, and working on that, some are working to to change the features.